To provide a system identification device which can identify the moment of inertia, viscous friction, and Coulomb friction of a motor coupled with a load having a limited movable range in a very small range with high precision, and to provide a motor controller equipped with the system identification device.

A system identification device comprising a system constant operating unit 103 for calculating a system constant identification value based on a position Fourier coefficient and a torque command Fourier coefficient and outputting the system constant identification value is further provided with a position Fourier converter 101 for calculating the position Fourier coefficient based on the motor position and outputting the position Fourier coefficient, and a torque command Fourier converter 102 for calculating the torque command Fourier coefficient based on the torque command and outputting the torque command Fourier coefficient.

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