To provide an actuator, which can attain a higher output with a small size by eliminating the effect of each of component accuracy and assembling accuracy.

The actuator is provided with a link mechanism by an telescopic and rotatable arm to transmit and output power. Since the arm is operated, even if a relative positional relation between a ball screw shaft and an output shaft is changed, so as to absorb the change, the power can be efficiently transmitted with minimized transmission loss of the power by a ball screw and the link mechanism. Thus, the actuator can attain high output in spite of a reduced size.