PURPOSE: To simply and precisely lock and unlock a door through simplified structure, and to dispense with a large operating space secured on the back side of the door by forming a latch bar in a linear sliding system.

CONSTITUTION: The back of a driving disc 3 is eccentrically provided with a driving projection 4, and the front of the driving disc 3 is provided with a driven projection 11 to engage with the operating projection 21 of a rotation- operating handle 20. A coil spring 6 is fitted in the annular groove 8 of the driving disc 3, and the front of a fixed main body 1 is provided with an inserting hole 10 for the rotation-operating handle 20, and the side of the fixed main body 1 is provided with a getting in and out hole for a latch bar 5. The inserting hole 10 is closedly shut by a cross-shaped shutter 9, and the driving disc 3 is inserted inside the fixed main body 1, and the latch bar 5 is provided with the driven projection 11 engaging with the driving projection 4. A resetting compression coil spring 7 is inserted between the latch bar 5 and the inner wall face of the fixed main body 1, and a back cover 2 is inserted into the rear part of the fixed main body 1 and fixed, and when the driving disc 3 is rotated by the rotation-operating handle 20, the latch bar 5 is plunged into the fixed main body 1.