An opening mechanism has a guide mechanism which holds the movable body in such a manner as to be slidable in the predetermined direction with respect to the planar solid body. This structure allows the solid body, the movable body and the guide bodies to be made of planar materials such as a steel plate, thereby enabling the opening mechanism to have a thinner profile. In addition, these components can be produced by a comparatively simple process such as press working, making it possible to provide a less expensive opening mechanism. A thin electronic device using this opening mechanism is also provided.