a doze warning system has a circuit 20 for producing pulse signals representative of left - and right - hand steering angle variations , circuits 30 and 40 counting the pulse signal and producing a warning signal when the counter value reaches a threshold value , and a circuit 60 for producing a reset signal to clear the counter value when a difference between a number of pulse signals representative of the left - hand steering angle variations and a number of pulse signals representative of the right - hand steering angle variations exceeds a given value , or of a condition wherein the left - hand or right - hand pulse signals inputted exceeds a predetermined pulse number . the reset signal generating circuit detects a steering angle variation in excess of the threshold value in a normal driving condition such as passing through a curved road and produces the reset signal to inhibit production of the warning . by this reset signal generating circuit function , the warning system is prevented from malfunctioning .