To increase the catch force of a door without disabling long-time usage of a torsion coil spring and making a structure larger as a whole by setting the elastic pressure contact position of the cam of a link plate to the bent outside.

A door-side mounting member 1 fixed to a door A is connected to a side-plate-side mounting member 2 fixed to a side plate B via a link plate 3 in a rotationally movable manner. Part of the link plate 3 is elastically pressurized by the arm 6a of a torsion coil spring 6 to generate catch force at the open/closed position of the door A. The arm 6a of the torsion coil spring 6 is bent from its way to the enlarging and opening direction to set the elastic pressure contact position of part of the link plate 3 to the bent end side.