The present invention relates to a computer having a standby power cutoff function for a peripheral device which can prevent a power loss by completely cutting off a standby current of a computer and a standby current of peripheral devices by cutting off a power supply to peripheral devices and a power supply unit when a computer is off. The power operation detection unit controls a power supply to the power supply unit by controlling the power cutoff switch unit by detecting an operation signal inputted from the power switch into the main board and for delaying and inputting an operation signal inputted from the power switch into the main board. The power loss due to a standby power can be prevented by cutting off a power supply to the computer and peripheral devices when a computer is off, with the help of a power cutoff switch unit which cuts off a power supply to the peripheral devices and the power supply by means of the power operation detection unit which detects an operation of the power switch.