Accessory, image pickup apparatus on which same is mountable, and camera system

A lens mount configured to be detachably mountable to a camera mount, wherein the camera mount includes a plurality of first bayonet claw portions and a plurality of first terminals, the lens mount comprising:

• a plurality of second bayonet claw portions configured to allow engagement with the plurality of first bayonet claw portions;
• and
• a plurality of second terminals configured to contact with the plurality of first terminals when the lens mount is mounted to the camera mount, wherein the plurality of second terminals is provided at positions that are different from positions of the plurality of second bayonet claw portions,
• wherein the plurality of second terminals includes a MIF terminal used in determination whether the lens mount is mounted on the camera mount, the determination being trigger that start supply of power from the camera mount to the lens mount, and
• wherein, when viewed in a central axis direction of the lens mount, a half line, that extends from a central axis of the lens mount and passes through the MIF terminal, passes through a predetermined bayonet claw portion among the plurality of second bayonet claw portions.