To increase the number of different keys of a cylinder lock.

This cylinder lock has an inner cylinder 1 with a plurality of slots communicating with a keyhole 2 and formed in a layered manner in two regions A, B facing each other with the keyhole 2 in between; an outer cylinder 16 rotatably fitted to the inner cylinder and formed with a locking groove 18 engaged with a locking bar 6; a plurality of first tumblers 9 enclosed in the respective slots belonging to the region A, energized in one direction and formed with locking step parts 12 at the inner edges facing the interior of the keyhole; and second tumblers 13 enclosed in the respective slots belonging to the region B and formed with engaging cutouts 15 at the outer edges to receive a protrusion 5 of the locking bar 6. When a key groove of a master key is engaged with the locking step part 12 of each tumbler, from the other direction, both ends of the first tumbler are adjusted to a shear line, and the engaging cutout of the second tumbler is adjusted to the protrusion of the locking bar.