To provide a pipe expanding apparatus with reduced frictional resistance which can adjust the length of an expanding part.

A rod 3 which is installed in a piston operated by a ram 1 and has a truncated cone with an inclined surface 5 extending in the tip direction, a pipe expanding member 11 consisting of frames which are installed around the peripheral surface of the rod 3 and have an inclined surface 18 which opens in the tip direction on the inside, and freely expandable/contractable ring members 25, 26 which are suspended on the periphery of the pipe expanding member 11 and converge each frame 10 expandably in the diameter direction are constituents. By a process in which the piston is operated, the rod 3 is retracted in the base end direction while the tip surface 1b of the ram 1 being pressed by the base end surface 12 of the pipe expanding member 11, the pipe expanding member 11 is expanded by the inclined surface 5 formed in the rod 3 to expand a pipe.