I purchased a vehicle for business use for one million yen in March 2022. Can I deduct this expense at one time from business income of this year?

Fixed assets that reduce in value in process of time such as buildings and vehicles are called depreciable assets.

Acquisition costs of depreciable assets are not deductible at a time in the year of purchase as necessary expenses. Instead, divided acquisition costs calculated by using depreciation methods can be deductible as necessary expenses for each year over the estimated usable period of each asset.

Legal durable years for tax purposes as estimated usable periods of assets and corresponding depreciation rates to be used for calculating a depreciation expense are stipulated in the Ordinance of the Ministry of Finance.

However, with regard to assets of which the estimated usable periods are less than one year, or of which the acquisition costs are less than 100,000 yen, you should deduct the full amount of acquisition costs at a time in the year when the assets are used for the first time for business.

For fixed assets acquired on and after April 1, 2007, depreciation methods such as Straight-line method and Declining-balance method are to be used for depreciation. And, for fixed assets acquired before that date, Former Straight-line method or Former Declining-balance method are to be used for depreciation..

However, you cannot use Declining-balance method or Former Declining-balance method if your fixed assets are as follows:
(a) Buildings acquired on and after April 1, 1998.
(b) Facilities attached to buildings and structures other than buildings acquired on and after April 1, 2016.
You have a choice of depreciation method with respect to each type of asset through a prior notification, or otherwise you should use statutory depreciation method. In the case of income tax for individual, Straight-line method or Former Straight-line method is generally applied.

(Example)
In the case of your question, if your vehicle is brand-new and for ordinary passenger’s use with a displacement of more than 660cc, legal durable years are 6 years. Depreciation rate of 6 years is 0.167 as for Strait-line method or 0.333 as for Declining-balance method.

Calculation method of depreciation for the asset acquired on and after April 1, 2007
Straight-line method Acquisition cost × Depreciation rate for Straight-line method
Declining-balance method Undepreciated balance × Depreciation rate for Declining-balance method ("depreciation amount before adjustment")
However, once the “depreciation amount before adjustment” falls below “guaranteed depreciation amount”, the following formula will be applied for the remaining years:
Revised acquisition cost × Revised depreciation rate
(Note 1) If you acquired or demolished fixed assets in mid-year, the depreciation amounts above should be apportioned by the ratio of the number of months during which the assets were used for business out of 12 months of the year.
(Note 2) “Guaranteed depreciation amount” refers to the amount calculated by multiplying the acquisition cost of the asset by the “guarantee rate” according to its legal durable years.
(Note 3) “Revised acquisition cost” represents the undepreciated balance at the beginning of the year in which the depreciation amount before adjustment first falls below the “guaranteed depreciation amount”.
(Note 4) “Revised depreciation rate” refers to the depreciation rate revised according to the legal durable years of the asset so that the depreciation amount for each year will be equal.
(Example)
In the case of your question, calculation of depreciation amount is as follows:
Straight-line method 2022 1,000,000 × 0.167 × 10 / 12 = 139,617 yen
2023 1,000,000 × 0.167 = 167,000 yen
Declining-balance method 2023 1,000,000 × 0.333 × 10 / 12 = 277,500 yen
2023  (1,000,000 − 277,500) × 0.333 = 240,593 yen

* Since you purchased (and began to use) the vehicle in March 2022, you need to apportion the depreciation amount for 2022 by the ratio of months of business use (10 months) out of a year.

<<Reference>>
Calculation method of depreciation for the asset acquired on and before March 31, 2007
Former straight-line method Acquisition cost × 90% × Depreciation rate for Former Straight-line method (Multiplication of 90% is not necessary for intangible assets such as fishing right and patents.)
Former declining-balance method Undepreciated balance × Depreciation rate for Former Declining-balance method
Undepreciated balance represents the amount obtained by deducting accumulated amount of depreciation expenses until previous year from the amount of acquisition cost. 
(Note 1) If you acquired or demolished fixed assets in mid-year, the depreciation amounts above should be apportioned by the ratio of the number of months during which the assets were used in business out of 12 month in the year.
(Note 2) After the year when an asset has been depreciated up to 95% of its acquisition cost, the amount of depreciation expense for each year will be obtained by dividing the amount equal to its remaining balance at the beginning of the following year minus 1 yen by five , so that 1 yen remains at the end of the 5th year.