To provide a constant water feeding interposition method capable of using endless connection pipe elements in the circumferential direction of a pipe.

This constant water feeding interposition method comprises a correction step for correcting the flat existing pipe 1 to a complete circular pipe, a generating step for generating cut pieces by cutting the corrected existing pipe at two positions apart from each other in the axial direction Y, a removal step for removing the cut pieces from a pipeline, an insert step for inserting a pair of right and left connection pipe elements 4 formed endlessly in the circumferential direction of the pipe from the radial outside of the existing pipe 1, and a moving step for moving the pair of connection pipe elements 4 slidably in the axial direction Y of the existing pipe 1.