PURPOSE: To improve burglarproofness by pivotally attaching a cam with a main lever to a pedestal while mounting a locking mechanism consisting of a combination lock and inhibiting the revolution of the cam with the main lever at the time of locking.

CONSTITUTION: A cam 3 with a main lever is composed of a cam heightened towards the right, and engaged with a catch on the opposite side at the time of the locking of a sash. The projecting section 21 of a sliding piece 20 is fitted simultaneously into three notched engaging sections 13A, 13B, 13C under a locked state. A sign display board 15 and a counter mark are conformed and operated to a predetermined numeric or mark of three columns under the state, and selecting pieces 12A, 12B, 12C are rotated and displayed through three engaging projections 11A-11C. At least one engaging section does not permit the fitting of the projecting section 21, and the sliding piece 20 is retained at a specified place. Since a retaining section 22 is fixed into a cam groove, the cam 3 is not revolved even when the main lever 4 intends to be tuned, thus resulting in a release-impossible state. Accordingly, the release of an intruder can be made remarkably difficult.