To prevent the fraudulent unlocking, so-called 'picking'.

This disk lock device comprises a key formed with key ridges in a recessed groove along the length direction of the side face of a key plate and a lock body 1 unlocked or locked when the key is inserted or removed. The lock body 1 is provided with a plurality of disks 30-34 in an inner tube 2 rotatably supported in an outer tube 3. Projections 13a-13d entering the recessed groove of the key are formed on the hole edges of the key insertion holes of the disks 30-33 of a first group, however no projection is formed on the key insertion hole of the disk 34 of a second group. The coupling with disk coupling grooves 14A and 14B is released when the projections 13a-13d hit the key ridges and are pressed in the radial direction on the disks 30-33 of the first group and the hole edge of the key insertion hole hits the side end face of the key plate and is pressed in the radial direction on the disk 34 of the second group.