To measure concentration of binary mixture gas we developed a new method that uses a Quartz gauge together with a capacitance manometer. Because a Quartz gauge's sensor is sensitive to both gas viscosity and gas pressure while a capacitance manometer is just sensitive to gas pressure, the viscosity of the gas can be estimated from pressure indication from both the gauges. If the gas is binary mixture gas and the viscosity of the gas changes monotonically with the concentration, the pressure deviation will give the concentration of binary mixture gas. This method has several merits. One is that we can apply to explosive gases because the sensors do not have any source to ignite such as a heated wire, an energetic light, and an electron source. The other is that because of no source to decompose the gas, this method does not change the concentration of the sample gas after the measurement. Then it is not necessary to discard the sampled gas, and consequently the effective amount of the sample is negligible.