To provide a cutting knife in which the structure of a is simplified protecting the edge of a blade by pressing the back side thereof onto the inner wall surface of a sleeve member so as to secure a space between the blade edge and the inner wall surface of the sleeve member.

A slider 50 is provided with first and second projections 54 and 58 at the front and rear ends with respect to the sliding direction thereof. The blade 1 is connected to the slider 50 by inserting either of the projections into the connecting hole 2 of the blade 1. The back side of the blade 1 is pressed onto the inner wall surface of the sleeve member 20 by setting 'the distance between the projections 54 and 58 and the back side inner wall surface of the sleeve member 20 when the slider 50 is loaded therein' smaller than 'the distance between the connecting hole 2 of the blade and the back side 1b of the blade 1'. The projections 54 and 58 are arranged on a straight line in parallel with the sliding direction of the slider 50, so that the pressing direction is also reversed when the slider 50 is reversely inserted into the sleeve member 20.