A 2-iminoimidazole derivative represented by the formula:
{wherein R1, R2 and R3 represent hydrogen, optionally substituted C1-6 alkyl, 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 salt thereof.