A power supply control device controls the supply of power via a switch circuit and a relay contact. If the semiconductor switches are on and the relay contact is off, when a switch temperature of the switch circuit is at least a relay ON-threshold, the relay contact is switched on, and the semiconductor switches are switched off. If the semiconductor switches are off and the relay contact is on, when a switch temperature of the switch circuit is lower than a relay OFF-threshold, the semiconductor switches are switched on, and the relay contact is switched off. The relay OFF-threshold is not more than the relay ON-threshold.