A power source control apparatus for use in electronic equipment of the type including a microprocessor and a main power source in the form of a battery controls a boosting circuit which boosts the output voltage of the battery to produce an operating voltage of the equipment. Connected in parallel to the battery are the boosting circuit and a power switch for producing a power ON/OFF signal. A reset/set flip-flop is connected between the boosting circuit and the power switch. The boosting circuit is operable only when the output of the flip-flop has a set state. Even when the power ON/OFF signal becomes a low level, i.e., OFF state, the flip-flop maintains its output in a set state until a power control signal is fed thereto from the external equipment. The period of time for which the operating power should be held after the turn-off of the power switch can be freely determined to suit the external equipment. Further, a reset signal generating circuit is provided for producing a predetermined reset signal depending upon the state of the flip-flop output.