The present invention relates to a diketohydrazine derivative of formula (I) and a pharmaceutically acceptable salt thereof (the symbols in the formula have the same meaning as described in the specification). ##STR00001## The compound of formula (I) has an inhibitory activity against cysteine protease, and it is useful for the treatment of inflammatory diseases, immune diseases, ischemic diseases, respiratory diseases, circulatory diseases, blood diseases, neuronal diseases, hepatic or biliary diseases, osseous or articular diseases, metabolic diseases, etc. And the compound has inhibitory activity against elastase and it is also useful for the treatment of COPD (chronic obstacle pulmonary diseases).