PURPOSE: To joint a rubber belt firmly in a short time, by exposing the porous resin sheets of both ends of the rubber belt, inserting unvulcanized rubber between the sheets, laminating them stepwise so as the fine hole parts of the sheets coincide with each other and press vulcanizing it.

CONSTITUTION: The rubber parts 2, 3 of the both ends of the belt in which a tensile member laminated with one or plural layers of a porous resin sheet 1 having many fine holes H and a thickness 0.1W1.0mm is embedded between upper and lower rubber parts 2, 3 are cut and removed by a length l necessary for joining, the sheets 1 are exposed and an adhesive is applied on the exposed parts and dried. Then, a thin unvulcanized rubber sheet R is inserted between the sheets 1 and a stepwise joint is shaped by making the fine hole H of the sheet 1 coincide with each other for laminating. Then, the concave parts of the joint are filled with unvulcanized rubber 2', 3', are pushed in an arrow direction and heated by the press plates P, P' provided with a vulcanizing mechanism and the flat and united joining part is shaped by connecting upper and lower rubber 2', 3' and rubber R through fine holes H of the sheet 1.