A power conversion apparatus has a structure in which the negative terminal of an insulated power supply is connected to one of connection nodes of a negative side bus with U-phase, V-phase and W-phase lower-arm switching elements except the end-side ones. That is the negative terminal of the insulated power supply is connected to the connection node between the negative side bus and the V-phase lower arm switching element to enable suppressing variations of input voltages supplied from the insulated power supply to respective drive circuits for driving the lower-arm switching elements by using low pass filters having smaller filtering capacity and smaller size.