A clutch-brake system in which at least one of clutch and brake devices has the following structure. A friction plate is mounted on a drive shaft to be synchronously rotatable on the drive shaft, but not to be movable in an axis direction of the drive shaft. First and second discs are provided on the opposite sides of the friction plate in the axis direction of the drive shaft, and movable in the axis direction. The first and second discs are synchronously moved in the opposite directions along the axis of the drive shaft, enabling to selectively switch between an operation state and a non-operation state.