To improve handleability by improving the operability of a slider 18 to a grip handle 1.

As for this blade replacement type cutter knife, an engaging projecting part 23 formed at the engaging spring 21 of a slider 18 is engaged with the guiding edge part 11 of the grip handle 1 with the moving operation of the slider 18 to make it possible to make a blade 26 project from the head port part 5 of the handle 1. The repulsion of the engaging projecting part 23 to a guiding edge part 11 in an engaged state where the engaging projecting part 23 is engaged with the guiding edge part 11 is set so that repulsion in a blade attaching and detaching area Q may be smaller than that in a slider moving area P. The moving resistance of the engaging projecting part 23 to the guiding edge part 11 in the engaging state is set so that moving resistance in a slider locked area R may be larger than that in the slider moving area P.