A gear mechanism and webbing retractor having a compact size in which a pinion is prevented from being damaged when a large initial driving force is applied from a gear. When a sensor detects an emergent deceleration of a vehicle, a piston driving device is actuated so as to move a rack at its standby position in a direction to a pinion. When the rack is located at the standby position, a tooth face on a side near a front end, of a front end tooth thereof is in contact with a pressure receiving surface of the initially driving member. The rack is moved along a pitch line in the direction to the pinion so that the front end tooth presses the pressure receiving surface. As a result, the initially driving member converts the initial driving force from the rack to a rotation force thereby rotating the pinion in the taking-up direction.