To provide a tire which allows a wheel chair to smoothly and safely elevate a step without any slip-down by absorbing a projection of the step in a round tire by freely controlling the pneumatic pressure in the tire.

Disks 4 having the diameter larger than the inside diameter of a tire 1 and smaller than the outside diameter thereof are installed on both sides of the doughnut-shaped rubber tube tire 1 through an axle, and the two disks 4 are pressed/separated against/from the tire. When a vehicle is traveling on a level ground, the pneumatic pressure in the tire 1 is adjusted to be maximum while the tire 1 is pressed by the disks 4 to the maximum. When a projection of a step bites the tire 1, the pneumatic pressure in the tire 1 is reduced by separating the two disks 4 from the tire, and a wheel chair is elevated while absorbing the projection of the step in the round tire 1.