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； R 1 represents an optionally substituted alkyl group or the like； R 2 represents a halogen atom or the like； and R 3 is an alkyl group substituted with an optionally substituted aryl group or the like, and R 4 is a hydrogen atom or the like； or R 3 and R 4 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.
