Provided are compounds of a formula (I) and their pharmaceutically-acceptable salts: wherein X1, X2 and X3 each independently represent N or CH; W represents the following formula (II): or the following formula (III): Y represents a group of a formula (IV): The compounds have a histamine-H3 receptor antagonistic or inverse-agonistic activity and are useful for remedy and/or prevention of obesity, diabetes, hormone secretion disorders, sleep disorders, etc.