A power supply switch wherein a contact operating member pivotably supported at its middle is coupled at one end to an end of a spring link and at the other end to an end of a tension spring, the spring link is coupled at the other end substantially to the center of a movable contactor which carrying on one end a movable contact for engaging with and disengaging from a fixed contact as well as the other end of the tension spring, and the movable contactor is formed to have on the other end a latch part to which a latch member is engageable as operatively associated with a bimetal plate for tripping the latch member to disengage it from the latch part, whereby the switch is made to break the contacts specifically upon detection of any excessive current, while sufficiently minimizing the size of the entire switch and improving the operability with an effectively reduced spring load applied during rocking operation of the operating member.