Abstract: [Problem] To provide a compound which may be used in treating diseases in which a calcium sensing receptor (CaSR) is concerned, particularly hyperparathyroidism. [Means for Resolution] It was found that novel pyrrolidine derivatives which are characterized by the possession of aminomethyl group substituted with arylalkyl group or the like, or salts thereof, have excellent CaSR agonistic regulatory activity and also have excellent selectivity with CYP2D6 inhibitory activity having a possibility of causing drug interaction. Based on the above, these novel pyrrolidine derivatives are useful as therapeutic agents for treating diseases in which CaSR is concerned (hyperparathyroidism, renal osteodystrophy, hypercalcemia and the like).