The controller area network (CAN) is one of the serial bus systems used in various applications, such as automobiles, airplanes, and industrial robots. This study focuses on analysis of electromagnetic interference (EMI) caused by a buck converter installed close to a CAN bus, and highlights the problems in a conventional EMI evaluation, followed by the development of an experimental EMI mitigation method. The verification experiments show that the periodic switching noise of a buck converter causes data-transmission failure in CAN. Finally, this study proposes a novel control method for a buck converter, which can mitigate EMI in CAN.