In order to provide unbalanced ringing when an exchange line card provides a balanced ringing output the interface provides a ringing detector in circuit with a customer pair. The contacts include a number of first contacts which are arranged in a row along a transverse direction of the insulative housing. The mounting portion includes first and second guide rails, and both side portions of the development cartridge respectively include first and second guide protrusions having different protrusion amounts from the both side portions to be respectively guided by the first and second guide rails. The control circuit can stabilize the mirror at relatively large tilt angles and, as a result, extend the available angular range beyond the snap-down angle.