To provide a cylinder lock having a simple structure which can realize the insertion and extraction of a key in a locked state, which makes the extraction of the key impossible in an unlocked state, and which can realize the attachment and detachment of an insertion/extraction regulating means which regulates the insertion and extraction of the key.

The cylinder lock 100 is provided with an outer cylinder 10, an inner cylinder 20, the insertion/extraction regulating means 30, a centering spring 40, a dead bolt 50, and a cover 60. The insertion/extraction regulating means 30 is constituted by a base part 30a corresponding to the shape of the engagement groove 12b of the outer cylinder 10 and a convex part 30b and can be attached to and detached from the engagement groove 12b by the engagement of the base part 30a with the engagement groove 12b. The inner cylinder 20 is rotatably engaged with and inserted to the outer cylinder 10, and a tumbler 22 having a notch 22b is movably arranged in the tumbler arrangement part 21 of the inner cylinder 20. In an unlocked state, the insertion/extraction regulating means 30 prevents the movement in which the tumbler is projected from the outer peripheral surface of the inner cylinder.