To provide a fastening structure of a fitting and high pressure hose used in a refrigerant circuit or the like of an air conditioner for a vehicle such as an automobile, capable of withstanding repeated tests of a pressurized impulse under a thermal cycle environment of a high temperature and a low temperature over a long period of time.

The fastening structure cramps and fastens the fitting 2 and the high pressure hose 5 inserted in a nipple 4 of the fitting 2. The high pressure hose 5 comprises an inner tube 5a formed of a rubber single layer, a resin single layer, or a resin layer having a rubber layer on an outer circumference, a plurality of rubber layers arranged on an outer circumference of the inner tube 5a, and a reinforcing layer 5b interposed between the plurality of the rubber layers 5a. A rectangular groove is formed on a tip end side outer circumference of the nipple 4, and a rubber band shaped ring 9 is attached on the rectangular groove. A groove part is formed on a rear end side outer circumference of the nipple 4, and adhesive 8 is applied on the groove part.