To securely prevent a danger that objects such as clothes, fingers or the like are caught at the time of the open/close operation of a panel.

The hinge unit 10 which connects the panels 1A, 1B to each other so that the panels 1A, 1B can be mutually rotated is provided to the upper end surface or the lower end surface at side edges of the adjacent panels 1A, 1B, and the side edges are reverse to each other. Then the hinge unit 10 fixed to each of the panels 1A, 1B is provided with fixed gear wheels 13A, 13B, a connection plate 12, and a pair of middle gear wheels 16A, 16B. Outer diameters of the fixed gear wheels 13A, 13B are smaller than board thicknesses of the panels, and the connection plate 12 retains the fixed gear wheels 13A, 13B at predetermined intervals. Then the pair of middle gear wheels 16A, 16B supported by the connection plate 12 are arranged between the fixed gear wheels 13A, 13B and engaged with each other.