PURPOSE: To form the inner surface at the end of a resin hose highly accurately to the predetermined shape and dimensions and, at the same time, simplify its manufacturing process and contrive to reduce its cost at its blow molding.

CONSTITUTION: By inserting parison 34, the diameter of which is smaller than that of hose main body 12, in the cavity 24 of a blowing mold 20 and then inserting a mandrel 28 in the parison 34 and finally clsing the blowing mold 20 so as to pinch the parison 34 between the outer surface of the mandrel 28 and the blowing mold 20 in order to form the end 14 of a hose. At the same time, by blowing air in the interior of the parison 34, the remaining part of the parison 34 is expanded radially outwards so as to form the hose main body 12, the diameter of which is larger than that of the end 14.