PURPOSE: To increase the throughput of the title device by measuring radiation concentration at a faster conveying speed than usual, inverting only the concen tration which is larger than a 1st set value in a conveyance direction, and deciding whether or not there is radioactive contamination with a 2nd set value at a normal conveying speed.

CONSTITUTION: The conveying speed of an article 3 by a roller conveyor 2 is made twice as fast as usual to feed it in an A direction, and the radiation concentration is measured by plastic scintillation detectors 5 and 6. It is decided whether or not there is the radiation contamination with the 2σ (standard deviation) of a background counted value for the measured values. Then when it is decided that there is no contamination, the operation is finished and when it is decided that there is the contamination, the article is fed in a B direction at a normal conveying speed and measured again to make a decision with 3σ. Here, if it is decided there is contamination, a warning is generated. Consequently, the processing speed is improved without lowering the reliability of contamination decision.