An electric power steering system includes: a band-stop filter 15a having a transfer function G1(s) for suppressing resonance, and a phase compensator 15b having a transfer function G2(s). The above function G1(s) is represented by an expression G1(s)=(s2+2ζ11ω1+ω12)/(s2+2ζ12ω1+ω12), where s is a Laplace operator, ζ11 is a damping coefficient, ζ12 is a damping coefficient, and ω1 is an angular frequency. On the other hand, the above function G2(s) is represented by an expression G2(s)=(s2+2ζ21ω2+ω22)/(s2+2ζ22ω2+ω22),where s is a Laplace operator, ζ21 is a damping coefficient, ζ22 is a damping coefficient, and ω1 is an angular frequency. Furthermore, the above damping coefficients ζ21, ζ22 satisfy an expression ζ2124 ζ22≧1.Thus, a filter such as a phase compensator may attain a design freedom while preventing the increase of arithmetic load, whereby both the suppression of resonance and a good assist response in a normal steering speed region, for example, may be achieved.