PURPOSE: To prevent the wrong of a cassette by providing a cut to the external shape of the cassette in parallel to the cassette inserting direction or a groove biased from the center line of the cassette and then forming a projection at a cassette slot in accordant with the cut or the groove.

CONSTITUTION: An original 2 is held between both frame bodies 1-A and 1-B of a cassette 100-a, and the screen part of the original 2 is exposed through a window 5. A groove 3-a is formed on the lower surface of the body 1-B at the left side of the center line set in the inserting direction of the cassette 100-a and in parallel to this inserting direction. Then a projection 4-a provided at a cassette slot 200-a can be slided into the groove 3-a. In such a constitution, the misloading like the adverse insertion, etc., of the cassette 100-a can be prevented and the correct position of the original 2 is kept for a scanner. Then the original 2 is correctly read.