To freely open and close a back door by the operation of a door handle by providing a two-way clutch mechanism having a means for locking rotation of a supporting point part and a means for releasing the lock state interlocking with the door handle operation of the back door on one of an opening and closing support point and a fulcrum of rotation.

A two-way clutch mechanism X is provided on the opening and closing support point of a back door. A lock means 12 is formed by a cam face 6, a circumferential face 2a and a roller 3 disposed between them, and a lock releasing means 13 is formed by a positioning means 14 comprising an engaging projection part 9 of a retainer 4 and a retainer fixing groove 7 of an inner ring 1 and the retainer 4. ON/OFF switching of external force F applied to the retainer 4 for switching between an operation mode of being free in the normal and reverse directions and a normal mode of locking in the normal and reverse directions is performed interlocking with the operation of a door handle. Thus, the back door can be freely opened and closed by the operation of the door handle.