An inner tubular portion (15) and an outer tubular portion (16) form an insertion space (14) of a plastic pipe (11) and are integrally formed on a joint main body (13). A cap (29) is connected to the outer tubular portion (16) by projection-recess engagement. A retainer mechanism (27) of the plastic pipe (11) is provided between the outer tubular portion (16) and the cap (29). A cutout portion (20) is formed in the outer tubular portion (16), and a bulging engagement portion (24) is arranged on the cutout portion (20). The outer periphery of the bulging engagement portion (24) is connected to the cap (29) by the projection-recess engagement. A restricting portion is provided between the cutout portion (20) and the bulging engagement portion (24). The restricting portion is composed of a first tapered surface (21) and a second tapered surface (25). The first tapered surface (21) is provided on the cutout portion (20) and decreases in width toward the outer end. The second tapered surface (25) is provided on the bulging engagement portion (24) and engaged with the first tapered surface (21).