PURPOSE: To prepare a rubber hose enhanced in the sealability at the engaging part of the terminal part of the rubber hose and a nipple, by using a mandrel having one or more annular projection in the molding of the rubber hose.

CONSTITUTION: A positioning cap 16 is inserted in a mandrel main body 11 having one or more annular groove 21 formed thereto up to a predetermined position from the terminal part thereof. Subsequently, a release solution is applied to the outer peripheral surface of the mandrel main body 11 and a rubber hose material 15 in an unvulcanized state cut into a predetermined length is externally fitted to the mandrel main body 11. A positioning cap 12 is inserted in the mandrel main body 11 on the rear end side of the rubber hose material 15 to fix the rear end side of the rubber hose material 15. After restraining members 17a, 17b are externally fitted to both end parts of the rubber hose material, said rubber hose material is vulcanized and molded. After molding, the rubber hose material 15 is penetrated in the annular grooves 21 formed to both terminal parts 11a of the mandrel main body 11 to form an annular projection 20. The restraining members and the mandrel main body are pulled off from a rubber hose main body 10 to prepare the rubber hose main body 10.