In a keyboard-equipped apparatus such as an electronic calculator, a plurality of gate circuits are provided which are enabled and disabled by key strobe signals and a common power supply control signal. The power supply control signal serves to initiate power supply from a power source to a central processing unit (CPU) and a display. The key strobe signals are developed from the CPU, with the respective levels being indefinite depending on or definite whether the central processing unit is appropriately powered. The power supply control signal is generated from a power controller. The actuation of a specified key included within a keyboard unit enables the power supply to the CPU and so on. The function of a conventional mechanical power switch may be eliminated because of the electronically controlled power supply control circuit.