The blockage detection mechanism includes a drive side gear portion, a pusher side gear portion, an insulating portion, a first contact portion, a second contact portion, and a temporary holding portion. The insulating part electrically insulates the drive side gear part and the pusher side gear part. The temporary holding part releases the holding of the pusher side gear part when the rotational resistance applied to the pusher side gear part becomes larger than a predetermined force.閉塞検知機構は、駆動側ギア部と、押し子側ギア部と、絶縁部と、第１接点部と、第２接点部と、仮保持部と、を備えている。絶縁部は、駆動側ギア部と押し子側ギア部を電気的に絶縁する。仮保持部は、押し子側ギア部に掛かる回転抵抗が所定の力よりも大きくなると、押し子側ギア部の保持を解除する。
