To provide a motor protector which detects the constraint and overload time of a rotor as well as cooling gas leak so as to protect the motor.

A motor protector is equipped with a switch 7 opening/closing in response to a flowing current amount and an atmospheric temperature, and a switch 6 opening/closing in response to only the atmospheric temperature, and the switches 6, 7 are connected to a power supply circuit of a motor to be protected 10 in series. The switch 7 is a thermostat using a bimetal disc 5, and the switch 6 is equipped with a bimetal disc 4 deforming in response to the atmospheric temperature and a movable arm 24 opened and closed according to the inversion of the bimetal disc 4. At the constraint and overload time of the rotor of the motor 10, the switch 7 is opened so as to shut off the power supply circuit of the motor 10 by the inversion of the bimetal disc 5, and at the time of cooling gas leak the power supply circuit is shut off by the inversion of the bimetal disc 4.