To reduce a machining cost of a damping force variable type actuator device for a shock absorber.

A screw shaft 11 is threadedly engaged with the screw hole 9 of a rotatably nut member 7 incorporated at the internal part of a housing 2 and a magnet 21 is mounted on the outer periphery of a nut member 7. A stator 22 of which a stepping motor 20 consists in cooperation with the magnet 21 is mounted on the outer periphery of the housing 2. The magnet 21 is arranged above the forming portion of the screw hole 9, an oil pressure release hole 24 to release the oil pressure of the closed end part of the screw hole 9 to the interior of the housing 2 is formed between the closed ends of the magnet 21 and the screw hole 9 and machining is facilitated.