PURPOSE: To simplify a structure and prevent the clogging of chips by forming a locking shoulder section cooperating with a tumbler on an annular body locked in an axial chamber of a polygonal head in a device provided with the tumbler in a cylinder lock.

CONSTITUTION: A cylinder lock 9 is extended into a polygonal head 5, it has a series of tumblers 10 in the form of a disk tumbler, and it cooperates with a locking fixed shoulder section 20. The shoulder section 20 is formed on an annular body R inserted into an axial chamber 21 of the polygonal head 5 and fixed to it. The number of the annular bodies R is equal to the number of the tumblers 10, and its inner diameter coincides with the inner diameter of a positioning cavity 12 for a lock housing 11. A recess 22 formed by the shoulder section 20 is coupled with the tumbler 10 to cooperate with it, and a gap (z) is left between the tumbler 10 and an annular end face 23. The structure can be simplified according to this constitution.