a system for driving a brushless motor comprises motor drive coils belonging to a plurality of phases respectively , a plurality of pairs of drive transistors connected to the drive coils respectively , a distribution circuit for sequentially distributing drive - coil energization switching signals to the plural drive transistors respectively , a slope synthesizer for smoothing leading and trailing slope portions of the drive - coil energization switching signals so as to apply the smoothed energization switching signals to the drive transistors respectively through the distribution circuit , a voltage - controlled oscillator for supplying a signal having a suitable frequency as an input to the slope synthesizer , a phase error detector for detecting the phase difference between counter - electromotive voltages induced in the drive coils and the drive - coil energization switching signals in a driver - coil energization pause period , and an error amplifier for amplifying the output signal of the phase error detector and applying the amplified phase error signal as an input to the voltage - controlled oscillator .