A numerical controller configured to control a machine tool for machining the workpiece on the basis of a machining program composed of a plurality of blocks includes a corner multiple curves inserting unit. This corner multiple curves inserting unit inserts, between consecutive two blocks, three cubic polynomial curves in which a position, a direction and a curvature are continuous and the distances from these two blocks are within a prescribed allowable tolerance, if a direction or a curvature between these two blocks is discontinuous in the machining program.