A telescopic actuator is adapted to be used on a right side or a left side of a body. The telescopic actuator includes a housing having a cylindrical shape and formed with an opening portion, an output rod supported inside the housing so as to be protrudable and retractable with respect to the housing, and a stroke sensor comprising a detectable portion provided on the output rod so as to be movable inside the opening portion of the housing and a detecting portion provided on the housing so as to face the detectable portion. A direction in which the detectable portion is eccentrically disposed with respect to a vertical plane including an axial line of the output rod is different depending on whether the telescopic actuator is used on the right side or on the left side of the body.