A power supply controller including a MOSFET between a power source and a load, a ground terminal, a gate driving circuit structured to control a gate potential of the MOSFET to turn on power and control the gate potential of the MOSFET to turn off power based on a ground terminal potential, and a turn-off circuit structured to switch the MOSFET into a turn-off state regardless of control by the gate driving circuit when the ground terminal potential is at a higher value than a source potential of the MOSFET.