PURPOSE: To prevent the flow inferiority of rubber by making the arranging position of a wear indicator at least at one place to coincide with the split position of a split mold to set the split position to an air outflow passage with respect to the wear indicator part at the time of vulcanization.

CONSTITUTION: A split mold 5 is formed from 9 tread sectors 5A-5I and the respective tread sectors 5A-5I are moved in the radius direction of a tire at the time of the completion of vulcanization to be perfectly detached from a vulcanized tire 1A. Wear indicator positions 11, 14 at two places with respect to the split positions 51-58 of the split mold 5 are allowed to coincide with the split positions 51-55 of the split mold 5. By this constitution, the split positions 51, 55 respectively coinciding with the wear indicator positions 11, 14 can be utilized as the air outflow passages with respect to the wear indicator parts at the time of vulcanization and the flow of rubber in the wear indicator parts at two places 11, 14 becomes well and flow inferiority is prevented.