An involute interpolation method for numerically controlled machining. The direction (G03.1) of rotation of an involute curve, amount or angle of moving, center position (XO, YO) of a base circle, and the radius (R) of a base circle are designated for interpolation on the involute curve at regular intervals of distance or angle. The process is executed by a numerical control apparatus and pulse distribution is continued so that interpolation on an involute curve can be performed without any particular programming device.