The provisions of Article 119, paragraph (4) of the new Act on General Rules for National Taxes apply to the calculation of the amount of penalty tax on national tax whose statutory tax return due date (for penalty tax for failure to pay, the statutory payment due date as prescribed in Article 2, item (viii) of the new Act on General Rules for National Taxes; hereinafter referred to as the "statutory tax return due date, etc." in this paragraph) arrives on or after October 1, 1987, and with regard to the calculation of the amount of penalty tax on national tax whose statutory tax return due date, etc. arrived before that day, the provisions then in force continue to govern.