An accessory mountable on and demountable from a camera body includes a first mount unit including a plurality of first bayonet claw portions, a second mount unit including a plurality of second bayonet claw portions configured to be engaged with the plurality of first bayonet claw portions, an elastic member configured to contact the camera body when the accessory is mounted on the camera body, and a holding member configured to hold the elastic member. The holding member is provided with a recessed portion which a part of the elastic member can enter when the accessory is mounted on the camera body.