To provide a concealed hinge in which two-way fine-adjustment functions among three-way fine-adjustment functions are built in a main body, and which has a one-way fine-adjustment function held in an external contact-type independent structure capable of being attached/detached as needed.

Three hinge arms 2 cross one another; the vicinities of the centers of the arms are turnably connected together; and ends of the arms, which are positioned on both the sides crossing each other, are housed in supporting parts, respectively. In this case, the ends 16 and 17 of the arms on one side are turnably held in the fixing positions of the supporting parts; the ends 16 and 17 of the arms on the other side are held in the state of being freely slidable in a specific direction along sliding holes 56 and 60 of the supporting parts; and relative positions of both the supporting parts are put into a parallel state from an opposed state by the motions of the arms. The supporting parts 3 and 4 of the arms comprise the supporting plates 5 and 6, sliding plates 7 and 8, and arm supporting bodies 9 and 10; the two-way fine-adjustment functions for two directions, that is, longitudinal and lateral directions are built in between the supporting plate and the sliding plate; and a fine-adjustment device 15 for the vertical direction of the independent structure is detachably brought into external contact with the side surface of the supporting plate, so that three-way fine-adjustment can be performed from a surface of the supporting plate.