In a motor speed controller, feedback control is implemented at a gain independent of the target rotational speed ωT while the increase in the circuit size or processing load is reduced. The rotational speed ω of the motor is controlled on the basis of a pulse signal in which a pulse period τP varies in inverse proportion to ω. A count clock generation circuit varies the clock frequency FC in proportion to ωT. The pulse period measurement section counts the count clock CLK during τP at the present ω and determines a measured count value C. The feedback filter inputs, as an error signal Ve, the difference between C and a target count value CN that corresponds to ωT, and generates an instruction signal to provide compensation for Ve. The feedback filter scales the instruction signal at a scaling factor that is proportional to ωT.