An automobile fan controller comprises: a fluctuation signal generator for generating a fluctuation signal; a pulse-width-modulation circuit including a triangle generator for generating a triangle-waveform signal having a constant amplitude and a constant period, and a comparator connected to the fluctuation signal generator and the triangle generator, for comparing the fluctuation signal with the triangle-waveform signal, thereby producing a pulse signal having a pulse width variable dependent on the fluctuation signal; and a driver circuit, including a switching power transistor connected to the pulse-width-modulation circuit, a fan motor mounted on an automobile, and an air flow switching unit mounted on the automobile for energizing and de-energizing said fan motor with a variable pulse width in response to the pulse signal. In this fan controller air flow delivered from an automobile fan driven by the fan motor can fluctuate at a fluctuation amplitude in response to an air flow range set by an automobile driver by connecting the automobile fan controller to the fan motor.