A warning device detects abrupt steering when the driver is dozing at the wheel and recognizes dozing of the driver to give a warning. The warning device comprises a sensor 20 for detecting steering variation angle, circuit 120, 130 for detecting abrupt steering based on detected right- and left-hand steering angle variations, and circuits 142, 146 for operating a warning means 30 when abrupt steering to the left and abrupt steering to the right are consecutively detected within a given period.