The present invention relates to an arylalkylamine compound represented by the following formula [I] or a pharmaceutically acceptable salt thereof, a process for preparing the same, and use of the above-mentioned compound as an activating compound (CaSR agonist) of a Ca sensing receptor, a pharmaceutical composition containing the above-mentioned compound as an effective ingredient, etc. The symbols in the formula represent the following meanings: Ar: optionally substituted aryl or optionally substituted heteroaryl here, the cyclic portion of the heteroaryl is bicyclic heterocyclic ring in which 5- to 6-membered monocyclic heterocyclic ring containing 1 or 2 hetero atom(s) and benzene ring are fused; R1: a group selected from the group consisting of optionally substituted cyclic hydrocarbon group, and optionally substituted heterocyclic group; n: an integer of 1 to 3; X: single bonding arm, —CH2—, —CO—, —(CH2)m—CO—, —CH(R2)—CO—, —(CH2)p—Y—(C(R3)(R4))q—CO—, —NH—CO— or —N(R5)—CO—; in the above-mentioned respective definitions of the X, the bonding arm described at the left end represents a bond with R1; m is an integer of 1 to 3; p is an integer of 0 to 2; q is an integer of 0 to 2; Y: —O— or —SO2—; R2: phenyl or lower alkyl; R3, R4: each independently represents hydrogen atom or lower alkyl; R5: lower alkyl; provided that the ring portion of the group represented by R1 is neither naphthylidine nor partially saturated group thereof, and, when X is —CH2— or —CO—, R1 is not naphthyl.