Amidino compounds represented by the formula ##STR1## and pharmaceutically acceptable acid addition salts thereof are novel compounds and are useful as powerful antitrypsine, antiplasmin, antikallikrein and antithrombin agents. Having strong anti-C1 (C1r, C1s) activities and an anticomplement activity, they are also useful as anticomplement agents. These amidino compounds are prepared by usual esterification of carboxylic acid compounds represented by the formula ##STR2## with 6-amidino-2-naphthol and, if necessary, can be transformed into pharmaceutically acceptable acid addition salts thereof.