To reduce the full height of a latch device so as to reduce the fitting space thereof by scraping of both shoulders of a rear end of a fixed body of a cylinder lock so as to form a part having an elliptic cross section, and inserting this part having an elliptic cross sectioning a case main body from a receiver hole of a front surface cover plate so as to form an escape recessed part, in which a tip of a key is to be inserted.

Both shoulders of a rear end of a fixed body of a cylinder lock 5 are scraped off so as to from a part 17 having an elliptic cross section, and this part 17 is inserted into a receiver hole 18 of a front surface cover plate 1. The cylinder lock 5 is fitted in a circular through hole from a back surface side, and a case main body 2 is fixed to a back surface of a boor by a screw, and a bracket metal, with which a tip of a latch body 3 is to be engaged, is fixed to a fixed frame body by a screw. When a door main body is turned for closing, the bracket metal abuts on an inclined surface 25 of a cam at the end of the turn, and after the latch body 3 is slid backward, when the door is full closed, the latch body 3 is slid forward so as to lock the door. A key 7 inserted into the cylinder lock 5 enters an escape recessed part 9 of the latch body 3, and turns a rotor 11 so as to remove the latch body 3 from the bracket metal, and the door can be opened.