A compound represented by the following formula (I) or a salt thereof is provided: wherein X represents a halogen atom; R1 represents a hydrogen atom, substituted or unsubstituted C1-6 alkyl group, substituted or unsubstituted C2-6 alkenyl group, substituted or unsubstituted C2-6 alkynyl group, substituted or unsubstituted aromatic group, substituted or unsubstituted aralkyl group, substituted or unsubstituted acyl group, substituted or unsubstituted arylsulfonyl group, substituted or unsubstituted C1-6 alkylsulfonyl group, substituted or unsubstituted C2-7 alkoxycarbonyl group, or hydroxyl group; R2 represents a substituted or unsubstituted C1-21 alkyl group; R3, R5, and R6 are the same or different and represent a hydrogen atom or halogen atom; R4 represents a hydrogen atom or substituted or unsubstituted C1-6 alkyl group; and R7 represents a hydrogen atom or substituted or unsubstituted C1-21 hydrocarbon group. Also provided is a therapeutic drug for osteoporosis and an osteoblast activator comprising the compound or a salt thereof.