To easily discharge a film cassette from a cassette chamber by providing fixed projections inside the chamber which is pressed by the cassette so that the cover is bent outside the chamber.

A cover 58 is flexible, and provided with a fixed projection 104 adjacent to the inside of an annular lip 100 on the circumferential edge, and a fixed projection 106 which is arranged on the center of the cover 58 and spaced from the lip 100 in the radial direction. For pressing an actuator unit 60 and a film cassette 10 downward in a chamber 52, when a hand-operated insert tool 98 is inserted through an insert hole 56 and brought in contact with a first spur gear 72, the cassette is simultaneously pressed against the two projections 104, 106. As a result, the center part 108 of the cover 58 is bent or distorted toward the underside of the projection 106 and the outside of the chamber 52, and the annular lip 100 on the circumferential edge of the cover begins to separate from the annular groove 102 of the chamber 52, in the vicinity of the first projection 104.