To enable the guidance of a slider and a wound belt with a simple structure.

A single-shaft actuator is comprised of an almost cross sectional H-shape pillar 1 in which a recess 1a is formed extending toward the opposite face in the longitudinal direction, an idle pulley 5 installed in one end and a drive pulley 4 in the other end of the pillar 1, a motor 2 containing a closed loop control means to rotationally drive the drive pulley, the wound belt 11 stored in the recess 1a by engaging the idle pulley 5 and the drive pulley 4, and the slider 13 fixed to the wound belt 11 and provided with a roller in contact with a side wall 1b of the recess in the piller.