An actuator is provided for driving a turbocharging pressure control valve of a turbocharger. The actuator comprises a motor, an output shaft and a speed reduction mechanism for transmitting rotation of the motor to the output shaft by reducing a rotation speed. The speed reduction mechanism includes at least one gear having a shaft hole, a support shaft inserted into the shaft hole and holding the gear rotatably, and wall portions provided at both ends of the support shaft in a manner sandwiching the gear. The speed reduction mechanism further includes a wear powder holding portion provided radially outside an outer periphery of the support shaft and in at least one of two end portions of the shaft hole and the wall portions in a manner to hold wear powder or foreign substance without scattering.