An inner tubular portion (15) and an outer tubular portion 16 for forming an insertion space for a plastic pipe (11) are formed integrally with a joint body (13). Two fitting grooves (17) are formed in the outer peripheral surface of the inner tubular portion 15. Two sealing members (18) for maintaining water-tightness in the gap between the plastic pipe (11) received in the insertion space and the inner tubular portion (15) are fitted in the corresponding fitting grooves 17. A pair of view windows (25) for visually checking the fitting grooves (17) and the sealing members (18), which are fitted in the fitting grooves (17), from the exterior are formed in the outer tubular portion (16). The view windows (25) are arranged at opposing positions.