Disclosed are pyridine derivative of the formula (I)

where R¹ and R² independently represent hydrogen or lower alkyl and R³ and R⁴, when taken separately, represent hydrogen, lower alkyl, alicyclic alkyl, substituted or unsubstituted polycyclic alkyl, substituted or unsubstituted aryl, or a substituted or unsubstituted heterocyclic group, or when together form a substituted or unsubstituted alicyclic N-containg heterocyclic group, pharmaceutically acceptable salts thereof. The compounds exhibit bone resorption inhibitng effect and are useful in the treatment of osteoporosis.