PURPOSE: To provide a stepping motor driven type linear actuator capable of accurately and easily obtaining the initial stroke position (physical starting point) of a rotor, having a small change of the starting point position during usage and an excellent durability without employing a large bearing by a thrust load resistance.

CONSTITUTION: A threaded shaft 14 is erected along the axial center in a housing 1, a rotor 3 is rotatably engaged with the shaft 14 to be rotated by a stator 2 to be axially reciprocated. An output shaft 8 is so supported to a second housing 10 rotatably but not axially displaceably, and biasing means 13 presses the shaft 8 to the end face of the rotor 3 via a ball 12. Thus, the linear motion upon rotation of the rotor 3 is converted to a linear motion without rotation of the shaft 8, and the shaft 8 is axially reciprocated by the stroke amount proportional to the number of stepping drive, i.e., the accumulated pulse voltage of the rotor 3.