Exhaust gas dilution device and PM measurement system

The present invention is one that, in measurement of exhaust gases respectively discharged from a first engine and a second engine, reduce a PM measurement error caused by sharing a dilution tunnel, and has: a dilution tunnel 2 for diluting exhaust gas from an engine with dilution air; a diesel exhaust gas introduction path 3 that introduces diesel exhaust gas from a diesel engine DE into the dilution tunnel 2; and a gasoline exhaust gas introduction path 4 that introduces diluted gasoline exhaust gas from a gasoline engine GE into the dilution tunnel 2, wherein: the dilution tunnel 2 has a gas mixing part 21 that mixes the diesel exhaust gas introduced by the diesel exhaust gas introduction path 3 and the dilution air with each other; and the gasoline exhaust gas introduction path 4 introduces the gasoline exhaust gas into an upstream side of the gas mixing part 21 in the dilution tunnel 2.