This is a multi-center double-blind parallel-group study in involutional osteoporosis patients to compare the efficacy and safety of monthly oral intermittent formulation ONO-5920/YM529 with its daily formulation.

Inclusion Criteria:

• Patients whose bone mineral density is <70% of Young Adult Mean (YAM), or <80% of YAM who have fragile fracture history
• Patients can walk on his/her own
• Written informed consent has been obtained from the patient.

Exclusion Criteria:

• Sequential osteoporosis patients or patients with other disorders showing low bone mass
• Patients with the findings that influence measurement of lumbar vertebral bone mineral density by the DXA method
• Patients who are unable to keep raising or standing for ≥30 min
• Patients with peptic ulcer
• Patients who have experienced anamnesis or gastrectomy (total extraction)