A power source supply control device includes controllable switch units configured to switch provision or non-provision of power source electric power supply to respective loads from a main power source, load monitor units configured to monitor a state in each of one or more of the loads connected to downstream sides of switch units, and a switch control unit configured to control on/off of each of the switch units sequentially, based on monitor situations of the load monitor units, in which the switch control unit specifies an energization switching order to the loads according to a predetermined state.