To reduce the cost while reducing the number of parts item and assembling man-hours by regulating the movement of a boss part in the axial direction while pinching an inner and an outer end surface of the boss part with a loose- out stopper lock piece and an abutment piece provided in a hose connector, and regulating the rotation while fitting a fixing projection in a fixing recessed part of the boss part, and fixing it with one operation.

A cylindrical fitting part 30 of a hose connector 3 is provided with loose-out preventing lock pieces 31, 31 and a flange-like abutment piece 32, and an elastically deformable fixing projection is projected from the inside of the abutment piece 32 at positions expressed with marks 39, 39. When the lock pieces 31, 31 are inserted into the boss part 13 through large diameter recessed parts 34, 34, the fixing projection of the abutment piece 32 is fitted in starting ends 36a, 36a of guide grooves 36, 36 and while the abutment piece 32 abuts on the outside of the boss part 13. In this condition, the abutment piece 32 is turned, and the fixing projection is rotated for movement to end parts 36b, 36b of the guide groves 36, 36, and fitted in the fixing recessed parts 37, 37. With this structure, the loose-out preventing lock pieces 31, 31 are rotated and locked with the inside end surface of the boss part 13.