A spin-polarized scanning tunneling microscope (STM) using a GaAs tip has been studied to observe the magnetization with nanoscale resolution for a sample magnetized in the plane of the film. A STM image of Si(111) 7×7 surface reconstruction using the GaAs tip was observed clearly under ultra-high-vacuum conditions. We found that the cleaved GaAs tip has a capability of high atomic resolution. Next, circularly polarized light irradiated the GaAs tip, and the I–V characteristics were measured for magnetic Ni80Fe20 and nonmagnetic Au samples. Changes in the tunneling current, which is estimated to be approximately 7%, were observed only for the NiFe sample under the circularly polarized light irradiation. It suggests that the change in the tunneling current is due to the spin-polarized tunneling from the GaAs tip to the NiFe.