A 2-iminoimidazole derivative represented by the formula:
wherein ring C represents a benzene ring, a pyridine ring, etc.; R1 represents optionally substituted C1-6 alkyl, etc.; R201 represents hydrogen, halogen, acyl, etc. ; R6 represents hydrogen, C1-6 alkyl, C1-6 alkyloxycarbonyl, etc.; Y1 represents a single bond,-CH2-, etc.; Y2 represents a single bond, -CO-, etc.; and Ar represents hydrogen, a group represented by the formula:
[wherein R10-R14 represent hydrogen, C1-6 alkyl, hydroxyl, C1-6 alkoxy, etc., and R11 and R12 or R12 and R13 may bond together to form a 5- to 8-membered heterocycle], etc.} or a salt thereof.