PURPOSE: To release the front lid of a cassette from its locked condition by only inserting the cassette into a cassette receiving base, by providing a projected part to the inner surface of the cassette receiving base.

CONSTITUTION: If a projected part 9 is installed to the inner surface of the side wall 2c of a cassette receiving base 2, the projected part 9 is just abutted with the front lid lock releasing pin 10 of a cassette 3 and pushes it when the cassette 3 is inserted into the cassette receiving base 2. Therefore, the front id 3a of the cassette 3 is released from its locked condition under a condition where the cassette 3 is inserted into the base 3. When the cassette 3 is taken out from the cassette receiving base 2, the front lid lock releasing pin 10 is released from the projected part 9 and projected and, as a result, the front lid 3a is locked.