An electric actuator is provided with a power transmission mechanism capable of converting a rotating driving power supplied from an electric motor to a reciprocating motion. This power transmission mechanism is provided with a cylindrical member formed, in its inner peripheral surface, with at least one row of rolling member rolling groove, a nut member disposed to be reciprocally through the rolling members endlessly circulating in the inner peripheral surface of the cylindrical member, and a cylinder rod operatively connected to an end portion of the nut member to be axially movable with respect to the cylindrical member. The reciprocating motion of the nut member in the axial direction is guided by the circular cylindrical member. According to such structure, high output and high controllability can be realized, as well as realizing of a compact electric actuator of a size similar to a conventional hydraulic cylinder.