To provide a power source control method which suppresses unnecessary power consumption of a power source part by controlling the operation period of an APO(automatic power-off) function and its APO time (specific continuance of an unused state) according to the state of electronic equipment.

A computer system is provided with an ineffective period wherein the APO function is made ineffective for a certain period after this system operates or equipped with a voltage drop detection part, and operation period control is performed by placing the APO function in operation, etc., only when the output voltage of a battery drops, namely, when the remaining electromotive force of the battery becomes small. Further, APO times are made settable by various application programs or time zones, and the APO function is made to operate with an APO time corresponding to an executed application program and the current time.