To provide an automatic wiper device for achieving a suitable wiping operation by suppressing a wiping operation for window glass due to a factor other than raindrops.

Weather forecast information corresponding to the current location of a vehicle 100 is acquired on the basis of current location information of the vehicle 100, and whether weather forecasted by the weather forecast is "rain" or weather other than "rain" is determined. Sensitivity when determining a rainfall state on the basis of raindrops detected by a raindrop detection sensor 3 is automatically adjusted in accordance with whether the weather forecasted by the weather forecast is "rain" or weather other than "rain", sensitivity when determining the rainfall state is increased when the weather forecast information forecasts rainy weather, and sensitivity when determining the rainfall state is decreased when the weather forecast information forecasts weather other than the rainy weather. A rainfall state is determined by the automatically adjusted sensitivity to operate a front wiper.