PROBLEM TO BE SOLVED: To provide technique capable of lightening patients load in inserting a balloon catheter in a body cavity.SOLUTION: A balloon contraction assisting tool 100 includes a hollow tubular part 110 having an opening 135 at least at one end 130. On an inner peripheral surface 112 of the hollow tubular part 110, a plurality of small-diameter parts 102 formed to be dispersed, and large-diameter parts 106 having larger diameters than the small-diameter parts 102, which are formed between the small-diameter parts 102, are arranged extending from one end 130 to the another end 120. The balloon contraction assisting tool 100 energizes inward an outer peripheral surface of a balloon at the small-diameter parts 102 of the hollow tubular part by pushing in the expanded balloon mounted on a balloon catheter from the opening 135 into the hollow tubular part 110 to thereby contract the balloon radially in section.
