A 2-iminopyrrolidine derivative represented by the formula: {wherein ring B represents a benzene ring, pyridine ring, etc.; R101–R103 represent hydrogen, halogen, C1-6 alkyl, etc.; R5 represents hydrogen, C1-6 alkyl, C1-6 alkoxy-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 heterocyclic ring], etc.}, or a salt thereof.