A resinous connector includes a flange-shaped base, a nipple, an O-ring, and an O-ring groove. The nipple extends from the base, and has an outer peripheral surface and sealing projections disposed on the outer peripheral surface. The sealing projections have a substantially triangle-shaped cross section whose diameter reduces in the direction away from the base. The O-ring is disposed between the nipple and a hose. The O-ring groove is formed at a root of the nipple in the outer peripheral surface, and is disposed at a position closer to the base than the sealing projection disposed in most proximity to the base. The resinous connector can inhibit the O-ring from being twisted or bruised by the hose.