1. A servo control system comprising: a target plant having a driver which is driven by a drive motor, a velocity detector that detects a velocity of the drive motor as a motor velocity (v); a position detector that detects a position of the drive motor or the driver as a driver position (x); and a position control apparatus that controls a position or a velocity of the target plant according to a position command value (Xc) commanded from a host device, wherein the position control apparatus is configured to: amplify a position deviation signal in which the driver position (x) detected by the position detector is subtracted from the position command value (Xc), to calculate a velocity command value (Vc); amplify a velocity deviation signal in which the motor velocity (v) detected by the velocity detector is subtracted from the velocity command value (Vc), to calculate a motor generated drive force (u 0 ); subtract a disturbance estimate value (^d) from the motor generated drive force (u 0 ), to calculate a corrected motor generated drive force (u c ); input the motor generated drive force (u 0 ) to a plant model equation in which the target plant is approximated by a lower-order model, to calculate a model velocity (vm), subtract the model velocity (vm) from the motor velocity (v), to calculate a disturbance estimate error signal (e); amplify the disturbance estimate error signal (e), to calculate the disturbance estimate value (^d); and output a control signal of the drive motor so that the corrected motor generated drive force (u c ) is generated, wherein an approximation error of the plant model equation with respect to the target plant in middle and low range frequency regions is smaller than an approximation error of the plant model equation with respect to the target plant in a high range frequency region, and a rate of amplification of the disturbance estimate error signal (e) in the middle and low range frequency regions is larger than a rate of amplification of the disturbance estimate error signal (e) in the high range frequency region.