A poor visibility estimation system that estimates poor visibility, comprising: a vehicle provided with a steering angle sensor adapted to detect steering angle of the vehicle, an angular velocity sensor adapted to detect steering angular velocity of the vehicle, a steering torque sensor adapted to detect steering torque of the vehicle, and a GPS adapted to detect position information of the vehicle; a change amount calculating section adapted to calculate an amount of change in the steering angle of the vehicle, an amount of change in the steering angular velocity of the vehicle, and an amount of change in the steering torque of the vehicle; and a visibility estimating section configured to estimate poor visibility and to identify a poor visibility point or area based on the calculated amount of change and the position information of the vehicle; wherein the change amount calculating section comprises a frequency converting section configured to calculate the amount of change of the steering angle by subjecting the steering angle of the vehicle to frequency conversion , and the visibility estimating section is configured to estimate poor visibility such that, if a spectrum area of the amount of change of the steering angle in a predetermined frequency band exceeds a prescribed reference that is an average of spectrum areas of steering angle data acquired in fine weather, the visibility estimating section is adapted to determine that the visibility is poor at a traveling point or in a traveling area of the vehicle for which the amount of change of the steering angle of the vehicle has been calculated; wherein the visibility estimation section is configured to use a frequency band from 0.5 to 1.0 Hz as the predetermined frequency band. a vehicle provided with a steering angle sensor adapted to detect steering angle of the vehicle, an angular velocity sensor adapted to detect steering angular velocity of the vehicle, a steering torque sensor adapted to detect steering torque of the vehicle, and a GPS adapted to detect position information of the vehicle; a change amount calculating section adapted to calculate an amount of change in the steering angle of the vehicle, an amount of change in the steering angular velocity of the vehicle, and an amount of change in the steering torque of the vehicle; and a visibility estimating section configured to estimate poor visibility and to identify a poor visibility point or area based on the calculated amount of change and the position information of the vehicle; wherein the change amount calculating section comprises a frequency converting section configured to calculate the amount of change of the steering angle by subjecting the steering angle of the vehicle to frequency conversion , and the visibility estimating section is configured to estimate poor visibility such that, if a spectrum area of the amount of change of the steering angle in a predetermined frequency band exceeds a prescribed reference that is an average of spectrum areas of steering angle data acquired in fine weather, the visibility estimating section is adapted to determine that the visibility is poor at a traveling point or in a traveling area of the vehicle for which the amount of change of the steering angle of the vehicle has been calculated; wherein the visibility estimation section is configured to use a frequency band from 0.5 to 1.0 Hz as the predetermined frequency band. <EOS>