To open or close a lock of a locking device in a simple manipulation and reduce the number of parts used for the device and increase the manufacturing efficiency.

A cum 201 which is clockwise and anticlockwise rotatable and machined in advance to have projections 207, 208, 209 is fixed to a knob together with an arm 206 pivoted to an opening/closing link 222 at one end thereof with a rotary shaft 202. Opening/closing plates 221, 222 are interlocked in accordance with the rotation of the cum 201 to open or close the lock. The projection 207 formed in the cum is engaged with one end of an arm 211 by the clockwise rotation of the cum 201 and the rotation of the cum 201 is restricted by the arm 211 to keep the locking device locked.