To provide a drain pipe regeneration method which can complete a whole process within a tolerable time without interfering with the life of a resident while the resident lives as usual, and which can line a drain pipe irrespective of a vertical main pipe, a horizontal main pipe, and a branch pipe continuously by a single apparatus and a single method.

The drain pipe regeneration method comprises: a step of inserting a spray gun device 10 into a small caliber pipe 13 from one terminal of a drain pipe to be coated and propelling the spray gun device with a propulsion device 14 and a direction control device until the spray gun device reaches a large caliber pipe 11; a step of reversely rotating the propulsion device 14 after the spray gun device 10 reaches the large caliber pipe 11 so that the spray gun device 10 is pulled from the pipe 11 toward the terminal of the small caliber pipe 13, while a liquid resin composition supplied from a gear pump device is ejected from a paint hose of the spray gun device 10 and simultaneously paint is ejected in the state of mist by pressure-feeding air from an air hose so that a resin coating film of a prescribed thickness is adhered to the inner surface of the pipe to be coated; and a step of drying and curing the resin coating film for the resin lining of the inner surface of the pipe.