PURPOSE: To simplify the structure and reduce the weight of an auxiliary tube inflating mechanism by inflating the auxiliary tube into the inner space of a tire to maintain a tire function when the internal pressure of the tire is reduced due to burst, etc.

CONSTITUTION: A rubber auxiliary tube 12 under contracted condition is installed on the outer periphery of a wheel rim 10 so that it faces toward an inner space 11 of a tire 1. A gas generating agent 13 for generating a combustion gas to inflate the auxiliary tube 12 is provided inside the auxiliary tube 12. When a pressure sensor 15 detects the reduction of internal pressure of the tire 1, an ignition control means 16 gives current to a squib 14 to ignite the gas generating agent 13, and the generated combustion gas inflates the auxiliary tube 12 into the inner space 11 of the tire 1. Thus, the internal pressure of the tire 1 can be maintained and a vehicle can travel continuously.