To provide a cutting angle adjusting method in a machining device for simply making high-accuracy adjustment at a low cost, an optical element forming metal mold for forming an optical element used in an optical communication module obtained by the device, and a cutting tool for it.

A shim SM having a predetermined thickness is interposed between the end face EP and the cutting tool T, thereby inclining a first edge part E1 at an angle δ to the end face EP. Thus, the extending angle of a cut part E3 is inclined at an angle γ to the end face EP, whereby a fine staircase-like structure can be cut with high accuracy.