A new index that applies the error root mean square method, which can discriminate and diagnose comprehensive pattern changes in multidimensional information, is proposed for assessing the environmental impact of a factory. The following possibilities have been confirmed : (1)In comparison with unit consumption evaluation, this index is less affected by increases and decreases in production, so it is more stable, can lead to quick and accurate environmental improvement actions, and can make such activities more efficient overall : (2)By diagnosing individual items, this method can target actions at a more limited set of specific items than before and motivate improvements in the factory itself, which leads to speedy and voluntary actions. The MT system approach can be applied not only to environmental impact assessments but also to daily activities of companies and other organizations to achieve more efficient operation.