Piperidine derivative or salt thereof

To provide a compound which can be used for treating diseases in which a calcium sensing receptor (CaSR) participates, particularly hyperparathyroidism. It was found that a novel piperidine derivative which is characterized in that one of a 3-position and a 4-position is substituted with an aminomethyl group substituted with an arylalkyl group or the like and the other position is substituted with aryl, heteroaryl or the like, or a salt thereof, has an excellent CaSR agonistic regulatory action, and also has excellent selectivity with a CYP2D6 inhibitory action having a possibility of causing drug interaction. Based on the above, this novel piperidine derivative is useful as a therapeutic agent for diseases in which CaSR participates (hyperparathyroidism, renal osteodystrophy, hypercalcemia, and the like).