To operate a mainbody under an operation desk and an accessory device while visually recognizing them by attaching a reversible L-shaped mouse pad to a drawer-type operation desk top part and containing an operation desk into a mainbody.

When a mouse 4 is used, the operation desk 6 is drawn by rails 7 and, in this state, it is operated and used on the L-shaped mouse pad 8 in the upper part of the operation desk 6. The L-shaped mouse pad 8 is not fixed by placed on the operation desk 6 so that usage is executed by the both of a right hander and a lefty by reversing and the cursor of the mouse is sufficiently moved in an X-Y direction even on the operation desk with a small area since the pad is the L-shaped mouse one. When an image from an electron microscope is only displayed in a monitor and, when using a personal computer in the lower part of the operation desk 6, the operation desk 6 is contained inside a desk 5 in order to pervent a hand from being hit by the operation desk 6 being a projecting object and also to execute arrangement compactly so that a personal computer mainbody and the accessory device under the operation desk are operated while visually recognizing them.