Proposed is a controller which can suppress an amount of protrusion of an operation member from an external surface of a chassis while operability of the operation member is maintained. A controller including a chassis, and an operation member which is slidable along an extension direction of the chassis with a predetermined position as a reference, and is rotatable in a circumferential direction of the chassis with the predetermined position as the reference, and at least a part of which is fitted into a recess section provided in an external surface of the chassis.