PURPOSE: To make it possible to injection-mold a swivel under the state that a swollen-out part loosely fits to the through holes of a leg part by a method wherein a recessed part for forming the central part of the swollen-out part and recessed parts, in which auxiliary molds are inserted, are formed on the surfaces of split main molds by employing the split main molds, on the surfaces of which recessed parts to form specified parts are provided and a pair of the auxiliary molds, at the tip of each of which a recessed part to form the side of the swollen-out part so as to put one of the split main molds upon the other and insert the auxiliary molds in the recessed parts in order to pour synthetic resin melt from a gate.

CONSTITUTION: By injecting synthetic resin melt through a gate 22 under the state that molds 20 and 20 are put one upon the other and auxiliary molds 21 and 21 are fitted into spaces formed by recessed parts 16a and 16a for auxiliary mold, a belt fitting body 1, which integrally has leg parts 10 and 10, and a swivel main body 2, which integrally has a neck part 13 and a swollen-out part 14 are simultaneously injection-molded under the state that the neck part 13 extends in a space part 11 and the swollen-out part 14 loosely fits to through holes 12 and 12 by means of recessed parts 1a, 3a, 4a, 5a, 10a, 13a, 14a and 14b for forming the belt fitting body 1, the swivel main body 2, a basic part 3, a hook part 4, an anti-unhooking piece 5, the leg parts 10, the neck part 13 and the central portion of the swollen-out part 14.