To accurately determine the life of a curved face machining tool even when machining a complicated curved shape.

This life determining method for the curved face machining tool in forming a curved face Q on a workpiece W by advancing the curved face machining tool with a cutter 2 at the end in a feeding direction F while being rotated comprises accumulating positional information for contact portions R1, R2,... RN of the cutter 2 with the curved face Q at positions F1, F2,... FN in the feeding direction F all over the feeding direction F and predicting the service frequency of the cutter 2 at each position from the accumulation results to determine the life of the curved face machining tool.