A motor drive device that is configured to convert direct current voltage of a battery into alternating current voltage using a power conversion circuit (10, 10C), thus driving an alternating current motor, the motor drive device including: the power conversion circuit (10, 10C) comprising four legs being connected in parallel between two direct current terminals, wherein each leg comprises a semiconductor switch element (101, 102) in each of upper and lower arms, and wherein each leg further comprises an alternating current terminal being an upper and lower arm connection point; a first switch circuit connected between the alternating current terminals of a plurality of first legs of the four legs of the power conversion circuit (10, 10C) and the alternating current motor; a second switch circuit (20b, 20b1) connected between the alternating current terminals of two second legs of the four legs of the power conversion circuit (10, 10C) and an alternating current power supply (1, 1a); a third switch circuit connected between the battery and the direct current terminals of the power conversion circuit (10, 10C); a transformer whose primary side is connected between the alternating current terminals of two transformer-sided legs of the four legs of the power conversion circuit (10, 10C), wherein each transformer-sided leg is different from each second leg; and an alternating current/direct current conversion circuit, which is connected to a secondary side of the transformer, and between a pair of output terminals of which the battery is connected, wherein, in a condition wherein the first and third switch circuits (20a, 20c) are turned off and the second switch circuit (20b, 20b1) turned on, the battery is charged by alternating current voltage of the alternating current power supply (1, 1a) being supplied to the power conversion circuit (10, 10C), high frequency alternating current voltage being generated, and the high frequency alternating current voltage being converted via the transformer and alternating current/direct current conversion circuit into direct current voltage and supplied to the battery, and in a condition wherein the first and third switch circuits (20a, 20c) are turned on and the second switch circuit (20b, 20b1) turned off, direct current voltage of the battery is converted into alternating current voltage by the power conversion circuit (10, 10C) and supplied to the alternating current motor. the power conversion circuit (10, 10C) comprising four legs being connected in parallel between two direct current terminals, wherein each leg comprises a semiconductor switch element (101, 102) in each of upper and lower arms, and wherein each leg further comprises an alternating current terminal being an upper and lower arm connection point; a first switch circuit connected between the alternating current terminals of a plurality of first legs of the four legs of the power conversion circuit (10, 10C) and the alternating current motor; a second switch circuit (20b, 20b1) connected between the alternating current terminals of two second legs of the four legs of the power conversion circuit (10, 10C) and an alternating current power supply (1, 1a); a third switch circuit connected between the battery and the direct current terminals of the power conversion circuit (10, 10C); a transformer whose primary side is connected between the alternating current terminals of two transformer-sided legs of the four legs of the power conversion circuit (10, 10C), wherein each transformer-sided leg is different from each second leg; and an alternating current/direct current conversion circuit, which is connected to a secondary side of the transformer, and between a pair of output terminals of which the battery is connected, wherein, in a condition wherein the first and third switch circuits (20a, 20c) are turned off and the second switch circuit (20b, 20b1) turned on, the battery is charged by alternating current voltage of the alternating current power supply (1, 1a) being supplied to the power conversion circuit (10, 10C), high frequency alternating current voltage being generated, and the high frequency alternating current voltage being converted via the transformer and alternating current/direct current conversion circuit into direct current voltage and supplied to the battery, and in a condition wherein the first and third switch circuits (20a, 20c) are turned on and the second switch circuit (20b, 20b1) turned off, direct current voltage of the battery is converted into alternating current voltage by the power conversion circuit (10, 10C) and supplied to the alternating current motor.