engagement with the stopper 6 of the cassette holder 2 when the stopper 6 takes a front position before cassette insertion the switch push member 9 is held by a regulating member 6c of the stopper 6 in a position for pushing turning on the insertion detecting switch 8 when the stopper 6 is urged more than a predetermined amount by insertion of a cassette the switch push member 9b is released from the regulating member 6c due to a rearward rotation of the stopper 6 and moves away from the insertion detecting switch 8 under the energy of the spring to turn off the switch 8 the side plate 3 includes an eject switch 10 located under a rear guide groove 5b the eject switch 10 is pushed into its on configuration by a guide pin 4b inserted in the guide groove 5b only when the guide pin 4b takes its front limit position when the cassette holder 2 begins its forward movement the eject switch 10 is released from the guide pin 4b and returns back to its off configuration the eject switch 10 unlike the other members is not provided on the other right hand side plate 3 not shown right and left insertion detection switches 8 8 and the eject switch 10 are connected in series so that a control means not shown activates the cassette loading driving motor to drive the right and left cassette holders 2 only when both insertion detecting switches 8 8 are turned off and the eject switch 10 is turned off succeedingly in fig1 reference numeral 11 denotes a connection plate bridging.