An image forming apparatus comprises a sensor, a base, a clamping section and a limiting section. The sensor includes a hook having a claw section. The sensor is held on the base. The clamping section and the limiting section are arranged on the base. The claw section is clamped with the clamping section. The limiting section is elastically deformable when the sensor is mounted on the base. When the claw section is clamped with the clamping section, the limiting section faces the hook from the opposite side of the clamping section so as to limit the position of the hook.