Abstract: A brushless motor speed detector requires no FG pattern or FG magnetization so that a motor structure is not restricted. The detector includes a simple detection circuit and a simple detection signal processing circuit, and is capable of obtaining a high-accuracy detection signal by using a variable signal output circuit for providing a signal alternately varied due to the rotation of a motor, a constant signal output circuit for providing a signal not varied due to the rotation of the motor, and a comparator for comparing an output signal of the variable signal output means with output signals of the constant signal output means or for comparing output signals of the first and second variable signal output circuit with each other to provide speed detection signals for one turn of the motor more than the number of driving magnetized poles.