A 2-iminoimidazole derivative represented by the formula: ##STR00001## {wherein R.sup.1, R.sup.2 and R.sup.3 represent hydrogen, optionally substituted C.sub.1-6 alkyl, etc.; R.sup.6 represents hydrogen, C.sub.1-6 alkyl, C.sub.1-6 alkyloxycarbonyl, etc.; Y.sup.1 represents a single bond, --CH.sub.2--, etc.; Y.sup.2 represents a single bond, --CO--, etc.; and Ar represents hydrogen, a group represented by the formula: ##STR00002## [wherein R.sup.10 R.sup.14 represent hydrogen, C.sub.1-6 alkyl, hydroxyl, C.sub.1-6 alkoxy, etc., and R.sup.11 and R.sup.12 or R.sup.12 and R.sup.13 may bond together to form a 5- to 8-membered heterocycle], etc.}or salt thereof.