法令翻訳 http://www.japaneselawtranslat...ky=&page=3

(退職所得についての選択課税)
第百七十一条  第百六十九条（課税標準）に規定する非居住者が第百六十一条第八号ハ（居住者として行つた勤務に基因する退職手当等）の規定に該当する退職手当等（第三十条第一項（退職所得）に規定する退職手当等をいう。以下この節において同じ。）の支払を受ける場合には、その者は、前条の規定にかかわらず、当該退職手当等について、その支払の基因となつた退職（その年中に支払を受ける当該退職手当等が二以上ある場合には、それぞれの退職手当等の支払の基因となつた退職）を事由としてその年中に支払を受ける退職手当等の総額を居住者として受けたものとみなして、これに第三十条及び第八十九条（税率）の規定を適用するものとした場合の税額に相当する金額により所得税を課されることを選択することができる。

Elective Treatment for Taxation of Retirement Income
Article 171  Notwithstanding the preceding Article, if a Nonresident as prescribed in Article 169 (Tax Base) is paid severance pay or other such compensation (meaning severance pay or other such compensation as prescribed in Article 30, paragraph (1) (Retirement Income); hereinafter the same applies in this Section) that falls under the provisions of Article 161, item (viii), (c) (Severance Pay or Other Such Compensation Arising from Work Carried Out in the Capacity of a Resident), the Nonresident may elect to have it deemed that the total amount of the severance pay and other such compensation that the Nonresident is paid in that year by reason of a separation from employment constituting a cause for its payment (or by reason of each separation from employment constituting a cause for payment, if the Nonresident is paid multiple packages of severance pay or other such compensation in the relevant year) has been paid thereto as if to a Resident, and to have income taxes imposed on the severance pay and other such compensation in line with the amount equivalent to taxes imposed when Article 30 and Article 89 (Tax Rates) are applied to the total amount of severance pay and other such compensation that the Nonresident is deemed to have received as a Resident.