To reduce the lowering of the adhesive strength between core wires and an adhesive rubber layer even if the vulcanizing time of a compressed rubber layer and the adhesive rubber layer becomes long in a transmission belt production method to manufacture a transmission belt improved in heat-resistant traveling life.

Adhesive treatment is applied to polyester core wires by a resorcin/formalin/latex (RFL) containing a chlorosulfonated polyethylene rubber and the treated polyester core wires are placed between an unvulcanized rubber sheets comprising an ethylene/α-olefin/diene rubber compound for forming the adhesive rubber layer. The unvulcanized rubber sheets are laminated on an unvulcanized rubber sheet comprising an ethylene/α-olefin/diene rubber compound for forming the compressed rubber layer and the whole is vulcanized under pressure and heating to vulcanize and bond the compressed rubber layer and the adhesive rubber layer both of which comprise the ethylene/α-olefin/diene rubber compound. In the transmission belt production method, at least one of an acid-receiving agent selected from magnesium oxide and calcium oxide is added to RFL or the unvulcanized rubber sheet for the adhesive rubber layer.