To provide a connecting tool of a resin tube having a simple constitution and capable of being easily handled and reduced in its manufacturing cost.

A plastic tube is constituted by integrally molding a diameter-reduced portion 11 and first and second connecting portions 12, 13 at both sides of the diameter-reduced portion, locking pieces 14, 15 bendable to inner and outer sides of opening portions are integrally formed on the whole outer peripheries of edge portions of the opening portions 12a, 13a, first and second sheath pipes 2, 3 having grooves 2a, 3a on outer peripheries can be respectively inserted into the opening portions of the first and second connecting portions, stepped portions 16, 17 as stoppers are respectively formed on boundary portions of both side portions in the diameter-reduced portion and end portions in the first and second connecting portions, and the locking pieces of the opening portions can be engaged with the grooves of the first and second sheath tubes.