A compressor includes: a case, a piston, an elastic member, and a drive. The piston in the case moves along an axis direction. The elastic member in the case applies a force to the piston to move the piston in the axis direction toward a first side of the case. The drive causes the piston to move in the axis direction toward a second side of the case. The piston includes a rack extending in the axis direction. The drive includes: a motor, and a pinion that rotates in accordance with the motor, and that is engaged with the rack. The pinion includes: first and second toothed regions each having a pinion tooth; and first and second flat regions having no pinion tooth. A number of the pinion teeth formed on the first toothed region is greater than a number of the pinion teeth formed on the second toothed region.