To reduce the number of work steps and ensure easy work in a short time by dividing a body of conventional cutter knife into a front part and a rear part, making the size of any one of the parts changeable to be slidable, and interposing a push spring therebetween in an integral manner with a cover.

A conventional cutter knife body is divided into a front part 1 and a rear part 2 and a push spring 4 is interposed therebetween, and they are integrated with a cover 3. A recess 5 and a projection 6 are arranged at an end of the front part 1 being a movable part so that a blade of this cutter knife exclusive for wall paper may always be in contact therewith in pressing the knife thereagainst. Under the condition, the end of the front part 1 having bamboo spatula and pallet effects is moved to cut the paper. Accordingly the cutting work can be made easily in a short time. The inside of a working bag can be kept in order with the compact knife, thereby improving the work efficiency.