When an alternating-current power is supplied to an ATX power supply, sub power is supplied to a PC board from the ATX power supply. When the sub power is supplied to the PC board, a PWOK signal is output to the ATX power supply by processing performed by a CPU according to BIOS, and main power is supplied to the PC board from the ATX power supply. Accordingly, the supply of the main power to the PC board and the starting processing of a gaming processing program are performed automatically, without any need for the conventional manual operation of a power supply switch, so that no effort is required for the starting of a slot machine.