PURPOSE: To obtain a system for producing an uncontaminated sample gas diluted at high accuracy.

CONSTITUTION: A main line 10 is provided with a flow rate sensor 16 and an exhaust gas flow rate control valve 15, fixed to an exhaust gas line 14, is controlled such that the flow rate sensor 16 will detect a preset flow rate of primary diluted gas. The primary diluted gas thus controlled is then admixed with a secondary diluted gas fed from a secondary diluted gas line 18 to produce a sample gas which is fed to the analyzer side through a sample gas supply line 20.