To provide a knife with a locking mechanism capable of not only taking a blade in and out of a handle but also performing the operation and release of the locking mechanism entirely with one hand in the knife provided with the locking mechanism for taking the blade in and out of the handle by performing turning to the handle and locking the blade non-turnably to the handle in a usable state.

An operation knob 11 for operating the locking mechanism is provided on a position operatable with the thumb of the hand holding the handle 2 at a part of the blade 9 and the operation and release of the locking mechanism are linked with the direction of force to be applied to the operation knob 11 so as to open/close the blade 9 to the handle 2. The thumb of the hand holding the handle 2 is hooked to the operation knob 11 and the force is applied in the direction of opening/closing the blade 9 to the handle 2.