Sp7 transgenic mice showed osteopenia due to the inhibition of osteoblast differentiation at a late stage, which was shown by woven bone structure in the cortical bone, reduced mineralization, reduced bone formation irrespective of the increased osteoblast density, and decreased expression of bone matrix protein genes especially Bglap2. Therefore, our experiments in vivo showed that SP7 inhibits osteoblast differentiation at a late stage and keeps the osteoblasts in an immature state. The gene discussed is SP7; the disease is Osteopenia.