To provide an apparatus for opening/closing a door of a case provided with a sidewise opened door in which a door body is able to be easily opened without a handle thereto or protrusion of the door body in a closed state from a case body, having an excellent appearance, and decreasing cost, in a box type case provided with a housing space inside the case body and the sidewise opened door body provided on at least one side face of the case body.

In this apparatus, one side edge of the door body 2 is rotatable by a hinge 3 and the other side edge is retainable onto the case body 1 by closing of a lock 4. Opening-helping means 5 are built in and provided on one or both of the upper and the lower edge parts near to the hinge of the door body in a direction of the thickness of the door body, wherein the means 5 are elastically energized in a projection direction toward a side of a box part 7 of the case body.