An electric power steering system includes a control unit configured to: compute an assist control amount (current amount), based on multiple kinds of state quantities indicating a steering state; control a motor based on the assist control amount, the motor being a source of assist force to be applied to a steering system of a vehicle; individually set, for the respective state quantities, limiting values that limit a variation range of the assist control amount, based on the respective state quantities used to compute the assist control amount; limit a value of the assist control amount using the limiting values; acquire a command value generated by a host control unit to change the assist control amount; and take the command value into account in setting of at least one of the limiting values, when executing control of the motor based on the assist control amount that reflects the command value.