A power factor correction device for three-phase AC-DC conversion enables effective correction and stable power conversion with a simple construction and control system. The device may include input terminals to which three-phase AC is inputted, and Positive and negative electrode terminals each connected to a load device. Transformers each have a primary coil with an end connected to the input terminals. Switching element(s) have ends applied with the voltage of another end of the primary coil, other ends connected to a common potential terminal on the side of the primary coil, and control ends. Rectifying devices have ends applied with the voltage of another end of the secondary coil so as to pass current flow into the positive electrode terminal. A smoothing condenser is disposed between the positive and negative electrode terminals. The control ends of the switching elements are controlled by a control signal having a constant duty ratio.