To provide a cutter knife capable of quickly and accurately linearly cutting the ridge line or the like of the folding part of a paper box or a convex surface like the surface of a bar-shaped material and a cylindrical material without using a ruler.

For this cutter knife with a guide, a air of the guides 3 are formed on the left and right interposing the blade tip of a planar blade 1 between them at the tip part of the holder 2 of the cutter knife and the guides 3 are made to abut on positions across the cutting line to be linearly cut of a material 4 to be cut. The holder 2 is composed of a main body part and a cap 21, a sliding groove is formed on a center line at the main body part, and by fitting the planar blade 1 to it, the planar blade 1 is housed in the holder 2, held and moved back and forth. The guides 3 stipulate the position of the cutting line and the depth of a cut at the time of linearly cutting the material 4 to be cut, to linearly cut especially the bar-shaped material, the cylindrical material and the chevron-shaped one like the fold of the paper box along the peak, and are formed symmetrically to the center line holding the planar blade 1 there between. When the guides 3 are abutted to the material 4 to be cut, the guides 3 are abutted to slopes on both sides across the pack of the material 4 to be cut and the blade tip of the planar blade 1 is positioned at the peak.