A power supply control device and a power supply control method capable of detecting a switch-related failure properly are provided. A power supply control device controls power supply via a switch. An output unit of a microcomputer produces a switching signal that instructs the switch to turn alternately on and off. A detection circuit reports a failure related to the switch if an accumulated period has reached or exceeded a threshold period. The accumulated period is accumulation of one or more periods when the switching signal instructs the switch to turn on but a comparator does not detectan on-state of the switch.