To part chips generated in a chamfering machining during the machining process and to shorten length of the chips, by forming a gradient linear portion for controlling a notch mount of cam curves of a pair of feed cams in a gradient linear shape having a plurality of stages having a plurality of horizontal portions in a constant interval.

A roller 34 of a cam follower is loosely fitted in a guide groove of feed cams 30, 31. When rotations of a pair of the feed cams 30, 31 change a fitting position between the roller 34 of the cam follower and the guide groove, the cam follower proceeds back and forth, stops, controls the back and forth movement of a cutter head spindle 27, and performs a chamfering machining of a steel tube. Cam curves forming a cam curve surface of the feed cams 30, 31 are gradient lines having a plurality of stages having a plurality of horizontal line portions. Thus, chips generated by the chamfering machining are parted.