To provide a device changing the composition of mixed gas inflating a tire by a program control and inflating the tire using air formed by reducing oxygen.

This device is provided with a first generating source 23 for main gas, a second generating source 28 for additional gas, a first compressor 25 suited to compress mixed gas of the main gas and the additional gas into a preset pressure, a dispenser for the compressed mixed gas connected to a delivery part of the compressor 25, a mixer 30 for the main gas and additional gas suited for carrying the mixed gas of prescribed components, a gas analyzer means 36 arranged in the downstream side of the mixer 30, a valve means 32 for controlling the flow rate between the mixer 30 and the first and the second gas generating sources 23, 28, and a program control means 45 controlling the valve means 32 according to the control signal from the analyzer means 36.