Abstract: The invention related to this application is: a method for folding back an opening end of resin pipe comprising following processes, (a) a process for mounting an annular body to a circumference of a pipe, (b) a process for inserting a conically protruded portion of a guiding portion including the conically protruded portion and a curved surface groove formed around this circumference to an opening end of the pipe and simultaneously advancing with rotating the guiding portion, and (c) a process for continuing the advancement with rotating the guiding portion whereby folding back the opening end of the pipe, and inserting the folded back pipe opening end to the circumference of the annular body; and an apparatus for folding back an opening end of resin pipe comprising a clamping element for holding the pipe and a bending element and the clamping element including a tightening mechanism for pushing the pipe to radial direction, and the bending element including a guiding portion for advancing by rotating with a