Recently, developments in neuroimaging technologies have facilitated a clearer understanding of the activation of sites in the brain. This technology is applied to brain-computer interface (BCI). A BCI is used to determine user intentions on the basis of brain activity and to display these intentions through the system. Previous BCIs have primarily used information on the brain activity related to the motor system. In this study, a BCI that assists motor functions on the basis of brain activity in the prefrontal cortex was experimentally developed and its validity was confirmed. The BCI system serves as a means by which a subject operates a robot. In addition, we propose the multi-support vector machine which is new clustering technology. In the experiment, brain activity was measured using near infrared spectroscopy (NIRS), and the data were acquired in real time. 17 subjects both male and female, participated in this experiment. As a result, 16 of them could control the robot. This result show a possibility of performing movement assistance in high accuracy and that it is possible to develop BCI systems can assist motor functions using information from the prefrontal cortex.