PURPOSE: To use a notched part formed on the lower surface of a cassette to prevent incorrect insertion of the cassette and to thin the structure of an apparatus by forming a bendable lever part having a hinge part on a cassette insertion part, and forming a prescribed guide part on the lever part.

CONSTITUTION: An elastic lever part 6 having the hinge part 7 and bending part 9 is supported bendably by a supporting part 8 of a fixed plate 4 of the cassette insertion part 3 and the guide part 10 is formed on one lever. If the cassette 1 is inserted in the reverse direction, the guide part 10 is depressed by the lower surface of the cassette and the bending part 9 is moved upwards to prevent the incorrect insertion. When the cassette 1 is inserted correctly, the guide part 10 is engaged with the inside of the notched part 2 of the cassette 1, the bending part 9 is butted on the lower surface of the cassette 1 and the lever part 6 or the like is deflected to insert the cassette 1. Consequently, it is unnecessary to form an incorrect insertion preventing means between the upper surface of the cassette and the apparatus body, so that the structure of the apparatus is thinned.