The present invention relates to a power conversion device and a power conversion system, and an object of the present invention is, particularly in three-phase/two-phase conversion, to suppress cost increase and conversion efficiency reduction by reducing the number of switching elements, and also to prevent generation of harmonics in a power supply. In order to achieve the object above, a power conversion device (1) includes input terminals (121 to 123), first output terminals (131, 132), second output terminals (141, 142), and an insulation transformer (11). The insulation transformer includes a primary coil (L1) and a secondary coil (L2) of equal inductance. The polarity of one end of the primary coil is equal to the polarity of the other end of the secondary coil. One of the first output terminals is connected to an input terminal and the one end of the primary coil. The other of the first output terminals is connected to an input terminal and one end of the secondary coil. One of the second output terminals is connected to the other end of the primary coil and the other end of the secondary coil. The other of the second output terminals is connected to an input terminal.