In this paper, we propose the control method of a peak shaving system for an electric injection molding machine (EIMM). The peak power shaver consists of a multiphase bidirectional dc-dc converter and supercapacitors (SCs), and is connected to a dc link of the inverter fed injection motor drive system of the EIMM. In the proposed control method, electric power is stored in the SCs through the multiphase bidirectional dc-dc converter with a PWM rectifier while the injection motor is at rest. When the injection motor is accelerating, the stored power in the SCs together with the power from the distribution feeders is supplied to the injection motor. Thus, the peak power can be shaved. The basic principle of the proposed control method is discussed in detail, then confirmed by digital computer simulation and experimental setup. The simulation and experimental results demonstrate that the peak power is shaved by 70% using the peak power shaving system.