PURPOSE: To simplify a mechanism so as to reduce a cost, by synchronously rotating a plural number of milling cutters on their own axes by a single motor through a planetary gear mechanism while simultaneously performing straight cutting off and revolutionary cutting of the milling cutter around a cut pipe by each separately equipped motor.

CONSTITUTION: If a worm 3 is rotated by a motor 34, a worm wheel 2 rotates, and a rotary sleeve 1 and a face plate 6 integrally formed with said wheel 2, are rotated, causing a cutter head 9 to perform revolutionary motion around a cut pipe P. While if a motor 8 is rotated, a ring gear 7 rotates to synchronously revolve four milling cutters 10 on their own axes via pinions 16→ bevel gears 15, 14→ spline shafts 13→ bevel gears 12, 11, thus cutting the steel pipe. Further if a motor 33 is driven, a timing gear 22 is turned through a belt 23, and a screw shaft 20 is turned to move a shifter 18. Accordingly, a wedge 28 is pressed inward by a roller wedge 27, and the cutter head 9 is moved inward, thus feeding the cutter 10 to cut the pipe.