A power conversion device comprising: an inverter that includes a plurality of switching elements to be on/off-controlled and drives an alternating-current motor by converting a direct-current voltage into an alternating-current voltage of an arbitrary frequency; an alternating current disconnecting switching unit that is connected between the inverter and the alternating-current motor; a current detector (11, 12, 13) that detects an output current of the inverter; and a controller that performs on/off-control of the switching elements in the inverter and switching control with respect to the switching unit, based on at least a current detected by the current detector, wherein the controller has a configuration to be able to interrupt a fault current by setting the fault current to a state of generating a current zero point, when the fault current containing a direct-current component is generated between the inverter and the alternating-current motor and wherein the power conversion device is characterized by further comprising a switching unit controller configured to open the switching unit after confirming, based on a current value detected by the current detector (11, 12, 13), the state that a current zero point is generated in the fault current, wherein the controller includes a fault determining unit having a current-zero point detector configured to compare the detected current value with a zero line to detect zero-crossing of the current value, and outputs a counter reset signal to a counter upon zero-crossing of the current value being detected, the counter counting up an oscillation signal of a constant cycle, a current value comparator configured to compare the counter value with a predetermined value, which is set from outside, to output a signal indicating that the current-zero point is not detected when the counter value is larger than the predetermined value, the predetermined value being changed according to a rotation frequency of the alternating-current motor or a fundamental wave frequency of a drive current of the alternating-current motor, and a determining unit configured to determine a switching element of the switching elements being in a short-cut fault state or remaining in an on-operation state based on the output signal from the current value comparator. an inverter that includes a plurality of switching elements to be on/off-controlled and drives an alternating-current motor by converting a direct-current voltage into an alternating-current voltage of an arbitrary frequency; an alternating current disconnecting switching unit that is connected between the inverter and the alternating-current motor; a current detector (11, 12, 13) that detects an output current of the inverter; and a controller that performs on/off-control of the switching elements in the inverter and switching control with respect to the switching unit, based on at least a current detected by the current detector, wherein the controller has a configuration to be able to interrupt a fault current by setting the fault current to a state of generating a current zero point, when the fault current containing a direct-current component is generated between the inverter and the alternating-current motor and wherein the power conversion device is characterized by further comprising a switching unit controller configured to open the switching unit after confirming, based on a current value detected by the current detector (11, 12, 13), the state that a current zero point is generated in the fault current, wherein the controller includes a fault determining unit having a current-zero point detector configured to compare the detected current value with a zero line to detect zero-crossing of the current value, and outputs a counter reset signal to a counter upon zero-crossing of the current value being detected, the counter counting up an oscillation signal of a constant cycle, a current value comparator configured to compare the counter value with a predetermined value, which is set from outside, to output a signal indicating that the current-zero point is not detected when the counter value is larger than the predetermined value, the predetermined value being changed according to a rotation frequency of the alternating-current motor or a fundamental wave frequency of a drive current of the alternating-current motor, and a determining unit configured to determine a switching element of the switching elements being in a short-cut fault state or remaining in an on-operation state based on the output signal from the current value comparator.