In a tire testing machine, a test tire transported onto a belt conveyor is entrusted to a lower rim by lowering the belt conveyor. In this state, an upper rim is lowered to the position of the lower rim, whereby the upper and lower rims are fitted to the test tire, and then the test tire is inflated. An inflation method for the tire testing machine comprises stopping the belt conveyor at an intermediate position, without lowering the belt conveyor to a descent limit, when entrusting the test tire to the lower rim by lowering the belt conveyor; and inflating the test tire, with the weight of the test tire being shouldered by the belt conveyor as well.