The purpose of this study is to evaluate the efficacy and safety of ONO-5920 in patients with involutional osteoporosis.

Inclusion Criteria:

1. Patients with fragility fracture according to the diagnostic criterial for the diagnosis of Primary Osteoporosis
2. Patients having radiographically confirmed vertebral (T4-L4) fractures
3. Other inclusion criteria as specified in the study protocol

Exclusion Criteria:

1. Patients having secondary osteoporosis or another condition that presents low bone mass
2. Patients having findings on X-ray that affect evaluation of vertebral fracture
3. Patients that have been administered bisphosphonate derivatives
4. Other exclusion criteria as specified in the study protocol