An introduction assistance instrument (11) is provided with a tubular body (13) that extends along a central axis and that is inserted into an organ having an introduction tube shape. The tubular body (13) comprises a tip section (21), a main body section (23), and a backup-providing section (25) that is provided between the tip section (21) and the main body section (23) and that includes one or more bent sections (25a, 25b). A side hole (27) is provided to one of the one or more bent sections (25a, 25b) and it is possible to introduce a medical instrument via the side hole (27) into a laterally branched tubular organ that branches from an organ having an introduction tube shape. In addition, at least one of the one or more bent sections (25a, 25b) is formed so that a contact location at which contact occurs with the inner wall of an organ having an introduction tube shape is created when the tubular body (13) is inserted into the organ having an introduction tube shape.
