A motor/generator comprising: magnetic field generating means for generating a first magnetic field, wherein the magnetic field generating means comprises a stator having a plurality of coils drive force outputting means for generating and outputting a rotary drive force using a first magnetic circuit formed by the first magnetic field, wherein the drive force outputting means comprises a first rotor member (4A, 4B), which is arranged to be rotated with respect to the stator using the first magnetic field; and a magnetic resistance changing mechanism (4C, 4D and 23A, 23B) for changing a magnetic resistance of the first magnetic circuit, wherein the first magnetic circuit is formed between the stator and the first rotor member (4A, 4B); and the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) comprises a mechanism arranged to change the magnetic resistance between the stator and the first rotor member (4A, 4B), characterized in that the magnetic field generating means is arranged to generate the first magnetic field and a second magnetic field, when energized with an electrical current having a first current component and a second current component to generate the first and the second magnetic field, respectively, wherein the stator is arranged to be energized with the electrical current having the first current component and the second current component to generate the first and second magnetic field (H1, H2); and the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) is arranged to change a magnetic resistance of the first magnetic circuit by using the second magnetic field, wherein the mechanism of the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) is arranged to change the magnetic resistance between the stator and the first rotor member (4A, 4B) using the second magnetic field. magnetic field generating means for generating a first magnetic field, wherein the magnetic field generating means comprises a stator having a plurality of coils drive force outputting means for generating and outputting a rotary drive force using a first magnetic circuit formed by the first magnetic field, wherein the drive force outputting means comprises a first rotor member (4A, 4B), which is arranged to be rotated with respect to the stator using the first magnetic field; and a magnetic resistance changing mechanism (4C, 4D and 23A, 23B) for changing a magnetic resistance of the first magnetic circuit, wherein the first magnetic circuit is formed between the stator and the first rotor member (4A, 4B); and the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) comprises a mechanism arranged to change the magnetic resistance between the stator and the first rotor member (4A, 4B), characterized in that the magnetic field generating means is arranged to generate the first magnetic field and a second magnetic field, when energized with an electrical current having a first current component and a second current component to generate the first and the second magnetic field, respectively, wherein the stator is arranged to be energized with the electrical current having the first current component and the second current component to generate the first and second magnetic field (H1, H2); and the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) is arranged to change a magnetic resistance of the first magnetic circuit by using the second magnetic field, wherein the mechanism of the magnetic resistance changing mechanism (4C, 4D and 23A, 23B) is arranged to change the magnetic resistance between the stator and the first rotor member (4A, 4B) using the second magnetic field.