PURPOSE: To ensure the steering stability without losing a comfort of ride by forming an upper filler by a foamed rubber material having independent bubbles with a foaming factor of 50% or less.

CONSTITUTION: A lower filler 10 is formed of a rubber having a JIS hardness of 80 to 95° while an upper filler 11 is formed of a rubber material having a lower JIS hardness than the lower filler 10. The upper filler 11 is formed of a foamed rubber having independent bubbles at a foaming factor of 50% or less. Therefore, the lateral rigidity of a vehicle including a car, a bus, and a truck during the vehicle runs in a condition of being mounted with a pneumatic radial tire 1 is secured mainly by the lower filler 10, by which the steering stability is enhanced. On the other hand, the longitudinal rigidity of the vehicle is suppressed by elastic deformation of the upper filler 11 as a whole while the vibration absorption action is rendered effective by the compression restoration of the independent bubbles, thus improxing the comfort of ride.