To cut a thin-thickness pipe having a relatively smaller diameter while using a ring gear and a planetary gear for moving an inner blade in the radial direction of the pipe while rotating it.

This pipe cutting device comprises the inner blade 3, a driving shaft 1, a connection shaft 2, an outer blade 4, the planetary gear 5, and the ring gear 6. The outer blade 4 has an inner peripheral face abutting on the whole outer peripheral face of a workpiece W in a predetermined axial range. The driving shaft 1 is coaxially and rotatably supported in the workpiece W, and has a through-hole 11 in an inside position a predetermined distance eccentric therefrom. The connection shaft 2 is rotatably supported in the through-hole 11. The inner blade 3 is rotatably held on an eccentric shaft 22 eccentric at the front end of the connection shaft 2, and arranged in the workpiece W. The planetary gear 5 is coaxially mounted at the rear end of the connection shaft 2 outside the workpiece W, and meshes with the ring gear 6. When the driving shaft 1 is rotated, the inner blade 3 is rotated while radially displacing a portion of the workpiece W, most protruded on the outer peripheral face in the radial direction.