An object of the present invention is to provide a method for preparing osteoblasts that are applicable, without causing risk of canceration, to bone defect repair or to the treatment of bone resorption, fracture, osteoporosis, or the like. To solve this problem, the present invention provides a method for preparing osteoblasts, the method comprising culturing mammal differentiated somatic cells in a medium in the presence of at least one compound selected from the group consisting of (1) statin compounds, (2) casein kinase 1 inhibitors, (3) cAMP inducers, and (4) histone methyltransferase inhibitors, to convert the somatic cells into osteoblasts.