PURPOSE: To surely perform power supply cut detection relating to a power supply cut detection circuit.

CONSTITUTION: A power supply cut detection circuit is composed in such a way as having a current control means 3 to be connected in series to a relay winding 1 and a voltage detection means 4 for detecting power supply voltage, as aforesaid in series connection and aforesaid voltage detection means 4 being mutually connected in parallel to aforesaid power supply voltage, and as aforesaid current control means 3 being turned to an OFF state so as to reduce the current flowing through aforesaid relay wiring 1 at least to be lower than the aforesaid first prescribed value when voltage detected by said voltage detection means 4 becomes lower than a second prescribed value.