The objective of the present invention is to provide an electric power converting device with which can executes a ground fault detection in a short time with its inexpensive configuration. In one step, the electric power converting device performs level comparison of a difference between output values of low pass filters, with a threshold value −E. If a W-phase is shorted to ground at a time when the U-phase and V-phase lower arm IGBTs are ON and W-phase upper IGBT is ON, the difference between the output values of the low pass filters and becomes small. In another step, a level comparison is made between the absolute value of a difference between the U-phase current value iu and U-phase current command value iu′, and a threshold value F. If the absolute value is lower than the threshold value, the result is determined to be normal, and if the absolute value is greater than the threshold value, the result is determined to be abnormal, because the U-phase is shorted to ground. In another step, a level comparison is made between the absolute value of a difference between the V-phase current iv and the V-phase current command value iv′, and a threshold value F. If the absolute value is lower than the threshold value, the result is determined to be normal, and if the absolute value is greater than the threshold value, the result is determined to be abnormal, because the V-phase is shorted to ground.