To provide a method which records the discharge amount of a contami nant etc. in exhaust gas together with time information and position information by a provable method and prove it.

A receiver receives standard time radio waves from standard radio wave transmission stations at two places. A contaminant measuring instrument 5 measures the concentration of the contaminant. The signals received by the receiver 3 and the signal measured by the contaminant measuring instrument 5 are inputted to a microcomputer 4 and converted into a specific signal or data by integrating the contaminant concentration together with the standard time, and the signal or data are recorded by a printer 6 etc. Further, the signal received by the receiver 3 is inputted to a microcomputer 7, which computes position information from the difference between two pieces of time information and similarly records it, so that the position can be proven. Instead of the standard time radio signals, time information or position information sent from a positioning satellite for GPS is similarly usable. The record is stored or sent to a proving institution and the contaminant discharge state is proven with it when necessary.