To facilitate the release by constituting a shaft to be constrained by the constraining arm of a drive shaft in such a manner as to be capable of engaging and disengaging, and providing a releasing operation lever on a cam drive shaft through the roller support arm of the drive shaft, a rock roller, and a cam cylindrical body.

When a door body is closed, its shaft A is guided into a U-shaped groove 13 to rotate a constraining arm 12 and a drive shaft 11, and a lock roller R in the clearance between cylindrical surfaces S1, S2 is bitten to stop and constrain the door body and a lock unit in a predetined position without play. When the lock is released, the eccentric cam surface of a cam cylindrical body 32 is moved by the OP directional tilting of a releasing operation lever 32, and an outer cylindrical surface block 22 fitted thereto is also finely moved in the OP direction and separated from the roller R surface to release the biting by the cylindrical surfaces S1, S2. A push-out arm 33 is also rotated clockwise, and the roller support arm 14 of the roller R is also separated by a pressing surface 37 to separate the shaft A from the U-shaped groove 13. Thus, the lock of a door can be released with a slight force.