the cover 24 is closed the recesses 28a of the actuators 28 urge the pins 34 and therefore the cassette 20 downwardly until terminals 50 at the bottom of the cassette 20 becomes inserted into a connector 52 on the housing 22 this sets up electrical connection of the cassette 20 to the housing 22 the relative position between the actuator 28 and its associated pin 34 sequentially varies as shown in fig4 a 4d during the course of such movements of the cover 24 as the cover 24 is opened from the position shown in fig4 a the lower edge of the recess 28a abuts against and lifts the pin 34 to the position shown in fig4 b the full open position of the cover 24 is shown in fig4 c in which the cassette 20 may be replaced with another as the cover 24 is moved toward the housing 22 from the full open position the upper edge of the recess 28a lowers the pin 34 in contact therewith as shown in fig4 d back to the full closed position shown in fig4 a the guide plate 48 carries a magnet 54 substantially at the center of its back surace the magnet 54 constitutes magnetic coupling means in cooperation with a magnetic metal sheet 56 which is adhered to a portion of an outer surface.