The present study was designed to investigate whether compressive mechanical strain affects osteoblastic cell differentiation. We developed a culture system with the multi channel that induces the mechanical stimuli with quantitative gradient strain on seeded cells during the culture. This culture system was a computer-driven device that the various mode of mechanical strains can be applied, using the pressurization or depressurization, to deform cells cultured on PDMS membrane. The mRNA expression levels of osteoblast-related genes, such as osterix, collagen type I, and osteopontin, determined by real- time PCR, decreased by the compressive strain. On the contrary, the expression of RANKL, a factor related to the induction of osteoclasts, increased in the compressive strain, while the expression of osteoprotegrin, a molecule that antagonizes the function of the RANKL, decreased in the same strain. It was suggested that the function of osteoblastic cells may be influenced by the compressive strain.