To provide a method of working a cutting blade of a tie-bar cutter by making a step of a groove width smaller.

A diamond blade 3 for groove grinding is used, which blade 3 includes a grinding wheel member 3b having a thickness in the rotation-axis direction in a range of 0.10 to 0.50 mm and each of both side surfaces of the member 3b forms a surface perpendicular to a circumferential surface of the member 3b, and a cemented carbide chip 2 on a working table 6 is notched so that a pre-groove having a width L1 that is narrower than a desired groove width Le is processed, and after the diamond blade 3 is retreaded from the chip 2, the blade 3 is moved so that a vertical side surface of the grinding wheel member of the blade is moved away by a distance of a width (Le-L1) and the pre-groove of the chip 2 is notched again by the blade 3 that is rotating to work the groove having a desired groove width Le.