Four bus bars, which are two positive-electrode-side bus bars connecting a positive electrode of a capacitor series circuit and a positive electrode of a power conversion section, a negative-electrode-side bus bar connecting a negative electrode of the capacitor series circuit and a negative electrode of the power conversion section, and an intermediate connection bus bar connecting in series two smoothing capacitors in the capacitor series circuit, are stacked in close contact with one another via insulating layers, to form a 4-layer bus bar. The two positive-electrode-side bus bars are not adjacent to each other and are connected in parallel to each other. The positive-electrode-side bus bar which is one of them and the negative-electrode-side bus bar are disposed adjacent to each other, thereby to reduce DC wiring inductances of the wiring structure in which the capacitor series circuit and the power conversion section are connected.