PURPOSE: To prevent the early abrasion of a seal member at low temperature by providing a pressure adjustment permitting/inhibiting means, which permits the pressure adjustment in case that the seal temperature gotten by a seal temperature getting means is more than the tolerable temperature, and inhibits the pressure adjustment in case that it is lower than the tolerable temperature.

CONSTITUTION: In case that a pressure adjustment permitting/inhibiting means 56 is in the mode of permitting pressure adjustment while a vehicle is not running even if seal temperature is low, if the seal temperature is low and the vehicle is running when the command to do pressure adjustment is issued, the start of pressure adjustment is inhibited, whereby a seal member is kept at atmospheric pressure. Next, if the vehicle is not running even if the seal temperature is low, the start of the pressure adjustment is permitted, whereby it turns out that the seal member is placed under high pressure. But, then, if the vehicle starts running, the pressure adjustment is inhibited if the seal temperature at that time is low. If the pressure adjustment is started, a passage opening/closing device 80 breaks a specified part passage from a tire chamber 6, and the seal member is placed under atmospheric pressure.