The provisions of Chapter VI, Section 2 (Penalty Tax) apply to national tax for which the statutory tax return due date (for penalty tax for non-payment, the statutory payment due date, and for national tax that has neither of these due dates, the day specified by Cabinet Order; the same applies hereinafter in this Article) arrives after the enforcement of this Act, and the imposition of the amount of penalty tax for understatement, the amount of penalty tax for failure to file, the amount of light penalty tax, the amount of withholding penalty tax and the amount of heavy penalty tax pertaining to national tax for which the statutory tax return due date arrived before the enforcement of this Act is governed by the former tax laws.