PURPOSE: To realize a detecting method of the state of distribution, by a method wherein a smoke emission inducing material is supplied to an exhaust pipe of a vehicle set in a wind tunnel, while an air flow is given around the vehicle, and a colored smoke discharged from a tail pipe is discriminated and observed.

CONSTITUTION: A supply port 5 of a smoke emission inducing material is provided in an exhaust pipe 3 of a vehicle 2, and the smoke emission inducing material is supplied from a supply device (wind washer device) 6, while an air flow is given around the vehicle by a blower. As for the smoke emission inducing material, a washer liquid is used therefore, for instance, and the washer liquid is jetted intermittently into the pipe 3 from the device 6. The washer liquid is burnt incompletely by an exhaust gas of high temperature, a colored smoke discharged from a tail pipe 9 is observed by viewing, and the state of distribution of the exhaust gas is detected therefrom. Accordingly, it is possible to dispose the exhaust pipe 3 appropriately and to provide an effective device for interrupting the exhaust gas, and the like.