An actuator includes a stepping motor; a multi-stage gear device including a first stage gear attached to a rotation shaft of the motor, wherein a gear of each stage engages with a gear of a next stage; and a base member on which the multi-stage gear device and the stepping motor are mounted, wherein in the multi-stage gear device, a grease composition for resin is applied to a bearing part of the gear, and to an engaging part between the gears, and the grease composition for resin includes: (a) a base oil including a poly-alpha-olefin oil with a kinematic viscosity at 100° C. of 4 to 6 mm2/s; (b) a thickening agent which is lithium soap; (c) a viscosity increasing agent; (d) a solid lubricant; and (e) an anti-wear agent, and wherein the NLGI consistency number of the composition is 00, 0, 1, or 2.