To provide an electric actuator capable of preventing an electro-mechanical output device from being damaged in case of the occurrence of an overload.

The electric actuator is characterized in that a toothed brake is fitted to the rotary shaft of a motor 4 driven based on the result of the arithmetic operation of an electric circuit for driving the motor to thereby operate an output shaft piston 2 by which loading is controlled; releasing the locking of the rotary shaft subjected to a controllable loading, while locking the rotary shaft subjected to uncontrollable overloading with the toothed brake. In such a way, overload can be supported, dispensing with the provision of a right structure to cope with the overload; thereby attaining a highly reliable load control preventing damage to the mechanism having the least strength to be adaptable for an ordinary control. Therefore, the miniaturization, light weight of the motor, power source, and electric circuit for driving the motor is attained at low cost and the mass and moment of inertia is made smaller, resulting in an ecconomical system. Furthermore, a regenerative power is suppressed from being generated due to overloading, thereby preventing damage to the electric circuit, etc., for driving the motor.