To solve a problem wherein a manual restoration type motor protector switch requires various bimetal materials, and cannot satisfy a restraint protection characteristic when securing an allowable maximum output condition in the case of a high-efficiency motor small in a ratio of an allowable maximum output current to a restraint current, it makes difficult to select a conformable protector, and it is difficult to turn off an electric circuit in a short time by a motion elimination operation of a particular bimetal.

By employing a structure composed by tightly thermally connecting, to a bimetal piece 1, a snap action bimetal 2 having an approximate specific temperature set higher than a heat generation temperature in a maximum rated operation current of the bimetal piece serially connected to a motor, the snap action bimetal senses the specific temperature and instantaneously operates, whereby safety protection can be applied to (1) a high-efficiency design motor small in ratio of an allowable maximum output current to a restraint current and (2) a high-output motor to which it is difficult to apply the safety protection in the past, and an application range can be expanded.