To eliminate the control instability of a converter due to detection error of the fundamental wave component of an input current, which occurs when the load state of converter is zero or light.

In a method for controlling a converter, the input current of a converter 2 is controlled with a power factor 1 of the converter 2, so that the input current follows active and reactive current commands iq* and id* (=0) which are obtained by executing a PI operation on a DC voltage deviation by means of a DC voltage control section 13, by executing current and voltage controls and computation by means of a current control section 18 from currents id and and iq, which are obtained by coverting the input current of the converter 2 by means of a p and q-axis coordinate transformation circuit 12 and the active and reactive current commands iq* and id* respectvely. In the method, a reactive current command computing section 14, which outputs the difference between a certain lower-limit set value and the effective current command value as the reactive current command when the effective current command value becomes lower than the lower-limit set value, is provided so as to eliminate the detection error of the fundamental wave component of the input current by increasing the input current by making a reactive current to flow somewhat, although the power factor 1 of the converter 2 becomes worse when the load of the converter 2 is zero or light.