The present invention relates to an agent for increasing BMD characterized by use of a cathepsin K inhibitor as a bone resorption inhibitor in combination with a type of PTH as a bone formation stimulator. This agent for increasing BMD is useful for the treatment of osteoporosis, bone fracture, arthritis, rheumatoid arthritis, osteoarthritis, hypercalcemia, osteometastasis of carcinoma, periodontal disease, bone Paget's disease and other bone metabolic diseases. For example, as the cathepsin K inhibitor, there can be mentioned a compound of formula (W) and a salt thereof, etc. ##STR00001##