An apparatus having an axial gap type motor/generator, the axial gap type motor/generator comprising: - stator means (6, 8, 9) for receiving alternating current, wherein the stator means (6, 8, 9) comprises a stator having a plurality of stator iron cores with a coil disposed on each of the stator iron cores; and - magnetic rotor means (1, 1A, 2) for rotating relative to the stator means (6, 8, 9), wherein the rotor means comprises a rotor facing the stator, with the rotor having a plurality of magnetic poles and wherein the stator means (6, 8, 9) and the rotor means (1, 1A, 2) are arranged in order to face each other along an axial direction with an axial gap; the apparatus comprising an alternating current control means for executing alternating current control of the alternating current flowing in the stator means (6, 8, 9), wherein the alternating current control means comprises a device configured to execute alternating current control of a multiple phase alternating current flowing in the coils; wherein: - the alternating current control means comprises a superpositioning control section that is configured in order to produce the alternating current by superpositioning a plurality of frequency components including a first order fundamental wave component and a plurality of higher harmonic wave components that have frequencies equal to integer multiples of a frequency of the fundamental wave components and are of orders that are equal to values of the integer multiples such that two pairs of the frequency components whose orders differ by two are superpositioned in the multiple phase alternating current, - a frequency component control section is provided which is configured to set coefficients of each frequency component to values that reduce a planar mode of vibration of the rotor in order to a prescribed degree, - coefficients of each frequency component are determined by referring to a map previously provided according to a number of the stator iron cores and a number of the magnetic poles of the rotor, - the order of the planar mode of vibration is equal to a difference between the number of the stator iron cores and the number of the magnetic poles of the rotor, - the planar mode of vibration comprises a vibration involving deformation of the rotor in an axial direction, and - the frequency component control section is configured to control a third order frequency component and a fifth order frequency component as the higher harmonic wave components. - stator means (6, 8, 9) for receiving alternating current, wherein the stator means (6, 8, 9) comprises a stator having a plurality of stator iron cores with a coil disposed on each of the stator iron cores; and - magnetic rotor means (1, 1A, 2) for rotating relative to the stator means (6, 8, 9), wherein the rotor means comprises a rotor facing the stator, with the rotor having a plurality of magnetic poles and wherein the stator means (6, 8, 9) and the rotor means (1, 1A, 2) are arranged in order to face each other along an axial direction with an axial gap; - the alternating current control means comprises a superpositioning control section that is configured in order to produce the alternating current by superpositioning a plurality of frequency components including a first order fundamental wave component and a plurality of higher harmonic wave components that have frequencies equal to integer multiples of a frequency of the fundamental wave components and are of orders that are equal to values of the integer multiples such that two pairs of the frequency components whose orders differ by two are superpositioned in the multiple phase alternating current, - a frequency component control section is provided which is configured to set coefficients of each frequency component to values that reduce a planar mode of vibration of the rotor in order to a prescribed degree, - coefficients of each frequency component are determined by referring to a map previously provided according to a number of the stator iron cores and a number of the magnetic poles of the rotor, - the order of the planar mode of vibration is equal to a difference between the number of the stator iron cores and the number of the magnetic poles of the rotor, - the planar mode of vibration comprises a vibration involving deformation of the rotor in an axial direction, and - the frequency component control section is configured to control a third order frequency component and a fifth order frequency component as the higher harmonic wave components.