To provide a polishing device of a long pipe inside surface, capable of preventing generation of an unpolished part in a step part of the long pipe inside surface.

This polishing device of the long pipe inside surface can freely insert at least an operation part 100 into a long pipe. The operation part 100 has a fixing means A to the pipe inside surface composed of an advancing-retreating operation rod 1a stored in a cylinder 1 and clamp arms 2 and 3 developable and foldable by an advance-retreat of this operation rod 1a, and a developable rotary brush means B installed on the tip of this fixing means A. A rotary brush 5 of the rotary brush means B is bendably formed in a horizontal plane in response to an inner diameter of the long pipe while maintaining a substantially horizontal state, by rotatably contacting with an inside surface of the long pipe in a substantially horizontal state by developing outward by rotation of a rotational driving device 4.