An improved evaporative fuel-purging control system for controlling a purging flow rate which is controlled by a solenoid purge control valve regulated with a pulse waveform signal. As for the characteristic of the purge control valve, differing periods of the signal differentiates the control valve linearity of purging flow rate with respect to the signal duty ratio. To improve the linearity, the pulse waveform signal period which creates the substantial linearity is selected among preset periods periods according to the preset duty ratio which works as a threshold value.