PURPOSE: To eliminate the dispersion of bonding strength as well as greatly improve the bonding speed of vulcanized rubber sheets by a method in which an olefinic thermoplastic resin film is interposed between vulcanized rubber sheets and they are melted and pressed by supersonic vibration.

CONSTITUTION: A 0.1mm-thick polyethylene film 3 of a melting point of 90°C is interposed in the joining portions of vulcanized rubber sheets 1 of a thickness of 1.5mm. The laminated sheets are joined at a bonding rate of 2.5m/min by a supersonic vibrator 5, a drive rotary roll 6 and a drive press roll 7 under the conditions of 350W outputs, 20kHz frequencies, and 30kg rolling pressure. Vulcanized rubber sheets with uniform joints can thus be obtained with high speeds.