PURPOSE: To improve the acuteness of a cut surface and form a groove in which a plate can be fitted tigftly, by arranging a number of projections at random on cutting straight lines in the X and Y direction, and installing a cutter in such an arrangement that it makes cutting motion while is deformed elastically in repetitions laterally about each cutting line.

CONSTITUTION: A cutter 26 moves along each cutting line in the X and the Y direction while is micro-vibrated up and down through the action of an eccentric cam 34, and performs cutting action for a plate-shaped work W. At this time, the cutter 26 penetrates the work W, and the cutting edge is received by a cutting mat 20. At the time of cutting in the X and the Y direction, the cutting edge of the cutter 26 passes those of a number of projections 40 on the cutting mat 20 which are located zigzagged or irregularly on the cutting line in the X or Y direction. In this process of passage, the cutter 26 is deformed elastically by the projections 40 in repetitions laterally about the cutting line. The cutting operation is thus performed under such a condition.