In a speed control system, there are provided a speed observer compensator (10) for inputting a difference between a speed V.sub.M of a mechanical system (5) and an estimated value V.sub.MO of a speed of the mechanical system (5) which is obtained by a speed observer (6) and outputting a speed difference V.sub.M-V.sub.MO based on the input, and a mechanical system model (8) for inputting a sum of an output of the speed observer compensator (10) and an output T.sub.ro of a PI controller (2), and the speed observer (6) is constituted in such a manner that the signal V.sub.MO produced after a passage of an output of the mechanical system model (8) through a filter delay element model (11) and a dead time delay element model (12) is equal to the speed V.sub.M of the mechanical system (5), and the output of the mechanical system model (8) is set to be a speed feedback signal V.sub.f of the speed control system. Consequently, it is possible to provide a speed control device capable of removing the high frequency component of the speed feedback signal, compensating for the phase delay of the delay element so as not to generate an oscillation having a high frequency, and causing the speed of the mechanical system to follow a target speed with high precision.