PURPOSE: To smooth the degassing at the time of vulcanization by forming a bent hole on a mold skeleton part by drawing off a metal member after forming a mold by using the core in which the metal member is inserted by forming a recessed part on the side wall of the groove in the same shape as the groove of a tread shoulder.

CONSTITUTION: Recessed parts 6, 7 are formed on the side walls 4, 5 of the numerous grooves 3 formed on the outer peripheral face 2 of a core 1, the tip of the metal member in taper shape is stud and inserted into the recessed parts 6, 7 as a small hole forming member. The core 1 is then surrounded by the main die 13 composed of a plate 11 and form 12 and a mold 15 is formed by pouring the molten metal into the core part 14. At this time the molten metal is poured in to the groove 3 as well and the center part of the small hole forming member 8 is cast to the skeleton part 16 of the mold 15. The mold 15 is then taken off and when the projecting member 8 is drawn from the skeleton part 16, numerous bent holes 17 are formed at the base end of the skeleton part 16. With vulcanizing a raw type by using this mold 15 the generated gas and air are flowed from the hole 17 and the raw rubber is also flowed in, but in case of taking off the type, the rubber is cut at its center, coming out of the hole 17 with the tyre.