Protector for electricity supply circuit

A protector for an electricity supply circuit includes: a power switch (11) capable to switch between connection and disconnection of the electricity supply circuit; a controller (12) configured to output a switching command signal to the power switch (11) in accordance with an input signal; and a current detector (11) for detecting current flowing to the electricity supply circuit. The controller (12) includes: a timer (22) for counting the time that passes after a load (RL) has been turned off, when the load (RL) is turned off by the power switch (11); and a mode switching unit (23) configured to switch the controller (12) to a sleep mode when a predetermined time (Q1) is counted by the timer.