The present invention relates to a novel pyrrolidine compound having melanocortin receptor agonist activity or a pharmaceutically acceptable salt thereof, and to pharmaceutical applications thereof. The present invention relates to a pyrrolidine derivative represented by formula [I], wherein ring A represents an optionally substituted aryl group or the like； R1 represents an optionally substituted alkyl group or the like； R2 represents a halogen atom or the like； and R3 is an alkyl group substituted with an optionally substituted aryl group or the like, and R4 is a hydrogen atom or the like； or R3 and R4 are terminally attached to each other, and together with the nitrogen atom to which they are attached, form an optionally substituted nitrogen-containing aliphatic heterocyclic ring that may partially contain a double bond； or to a pharmaceutically acceptable salt thereof.
