An electric power conversion device comprising: - a transformer composed of three or more windings (6a, 6b, 6c, 6d1, 6d2) magnetically coupled with each other, power supply sources (1, 11, 34) being connected to at least two of the three or more windings (6a, 6b, 6d1,6d2), a load being connected to at least one of the three or more windings; - a plurality of switching circuits (4, 8, 30) via which the at least two of the three or more windings (6a, 6b, 6d1,6d2) are respectively connected to the power supply sources (1, 11, 34), wherein the plurality of switching circuits (4, 8, 30) each include two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35}, characterized in that when one pair of the two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35)} is turned on, power is supplied to the at least two of the three or more windings of the transformer at a positive polarity for the winding connected to the corresponding switching circuit, whereas, when the other pair is turned on, power is supplied to the transformer at a negative polarity for the winding connected to the corresponding switching circuit; and - a control circuit configured to control the plurality of switching circuits (4, 8, 30), wherein the control circuit is configured to temporally divide, within one switching period, a total ON time during which power is supplied, in accordance with the number of the power supply sources (1, 11, 34) to supply power, the one switching period being a minimum repetitive period during which power is supplied alternately from the power supply sources connected to the at least two of the three or more windings of the transformer, and the control circuit is configured to allocate the temporally divided ON times to the pairs of switching elements of the plurality of switching circuits (4, 8, 30) connected to the power supply sources (1, 11, 34) to supply power, respectively, and the plurality of switching circuits (4, 8, 30) are configured to operate so as to supply power to at least one of load sides (11, 21, 34) from the power supply sources (1, 11, 34) connected to the respective switching circuits (4, 8, 30), during the temporarily divided ON times allocated by the control circuit. - a transformer composed of three or more windings (6a, 6b, 6c, 6d1, 6d2) magnetically coupled with each other, power supply sources (1, 11, 34) being connected to at least two of the three or more windings (6a, 6b, 6d1,6d2), a load being connected to at least one of the three or more windings; - a plurality of switching circuits (4, 8, 30) via which the at least two of the three or more windings (6a, 6b, 6d1,6d2) are respectively connected to the power supply sources (1, 11, 34), wherein the plurality of switching circuits (4, 8, 30) each include two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35}, characterized in that when one pair of the two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35)} is turned on, power is supplied to the at least two of the three or more windings of the transformer at a positive polarity for the winding connected to the corresponding switching circuit, whereas, when the other pair is turned on, power is supplied to the transformer at a negative polarity for the winding connected to the corresponding switching circuit; and wherein the plurality of switching circuits (4, 8, 30) each include two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35}, characterized in that when one pair of the two pairs of switching elements {(4a, 4d) and (4b, 4c), (8b, 9a) and (8a, 9b) or (8b, 8c) and (8a, 8d), (30a, 35) and (30b, 35)} is turned on, power is supplied to the at least two of the three or more windings of the transformer at a positive polarity for the winding connected to the corresponding switching circuit, whereas, when the other pair is turned on, power is supplied to the transformer at a negative polarity for the winding connected to the corresponding switching circuit; and - a control circuit configured to control the plurality of switching circuits (4, 8, 30), wherein the control circuit is configured to temporally divide, within one switching period, a total ON time during which power is supplied, in accordance with the number of the power supply sources (1, 11, 34) to supply power, the one switching period being a minimum repetitive period during which power is supplied alternately from the power supply sources connected to the at least two of the three or more windings of the transformer, and the control circuit is configured to allocate the temporally divided ON times to the pairs of switching elements of the plurality of switching circuits (4, 8, 30) connected to the power supply sources (1, 11, 34) to supply power, respectively, and the plurality of switching circuits (4, 8, 30) are configured to operate so as to supply power to at least one of load sides (11, 21, 34) from the power supply sources (1, 11, 34) connected to the respective switching circuits (4, 8, 30), during the temporarily divided ON times allocated by the control circuit.