A shield lock mechanism for attachment to a shell includes a holding member configured to be moved by an external operation between a holding position at which a shield is held and an attachment-detachment position at which the shield can be attached or detached, a biasing member configured to constantly bias the holding member toward the holding position, and a restriction member configured to be moved by an external operation between a restricting position at which movement of the holding member arranged at the holding position is restricted and a cancelling position at which the restriction is cancelled.