A device for vulcanizing vehicle tires uses a heating press and an internal bladder that is supplied with vaporous heating medium. In order to assure that the measurement of the vulcanization temperature is effected at the relevant locations of the internal heater, there is provided a temperature sensor in the form of a radiation thermometer or pyrometer that is disposed in the bladder cavity. The pyrometer takes an indirect temperature measurement for at least one location on the interior wall of the bladder by measuring a radiant energy emitted from the interior of the bladder.