In case of catching and quantitative-analyzing PM (Particulate matters such as soot or the like) contained in exhaust gas of, for example, a diesel engine by the use of a filter, an exhaust gas dilution device that dilutes the exhaust gas by adding air for dilution is used.
Conventionally, this kind of the exhaust gas dilution device extracts (samples) exhaust gas of an automobile and circulates the extracted exhaust gas to an analyzer through an exhaust gas circulation pipe as shown in, for example, the patent document 1 and the patent document 2. Then the exhaust gas is diluted by mixing the dilution gas to be supplied to the dilution gas supply pipe at a predetermined ratio in a mixing section arranged on the exhaust gas circulation pipe.
The dilution gas supply pipe makes a contact with the exhaust gas circulation pipe until the dilution gas is supplied to the mixing section or the dilution gas supplied from the dilution gas supply pipe passes a surrounding area of the exhaust gas circulation pipe.
With this arrangement, however, a temperature of the dilution gas rises because the dilution gas is affected from the temperature of the exhaust gas through the exhaust gas circulation pipe, or through the exhaust gas circulation pipe and the dilution gas supply pipe, then the exhaust gas can not be mixed with the dilution gas at a predetermined temperature, thereby having an effect on the analysis result.    Patent document 1: Japan patent laid-open No. 2002-333389    Patent document 2: Japan patent laid-open No. 2000-329661