When a highly accurate clock is received by a GPS radio wave from a GPS antenna, the highly accurate clock is always generated by locking a phase locked loop (PLL) circuit within a hold-over section of a clock control section in a power supply control unit. When the GPS radio wave cannot be received normally, the highly accurate clock depending on the GPS radio wave is set to a self-running condition not depending on a self-oscillation clock from an internal clock generating section and a time management section automatically corrects the present time data obtained when the standard radio wave is received from a radio wave antenna based on the highly accurate clock. A primary voltage generating section continuously generates the highly accurate clock even when an ignition switch is turned OFF by avoiding voltage variation in battery voltages while the ignition switch is turned ON. Accordingly, the power supply control device can sustain highly accurate time correction and a clock function under any environmental condition and can also control and execution of various functions based on accurate time management.