Disclosed is a compound of 3-{(2S,4S)-4-[4-(3-methyl-1-phenyl- 1H-pyrazole-5-yl)piperazine-1-yl]pyrrolidine-2-ylcarbonyl} thiazolidine (compound I) which is useful as a dipeptidyl peptidase IV inhibitor. This compound has excellent characteristics in stability and moisture absorption, while having a reproducible crystal structure. Also disclosed is a method for producing such a compound.