AUTOMATIC WIPER UNIT

PURPOSE:To prevent a window or the like from being wiped under dry condition, by changing a time interval for driving wiper blades on the basis of the previous time interval according to the integral value of rain drop detection output and the result of comparision between the first and the second discrimination levels. CONSTITUTION:Rain drops or the like are detected by means of a rain drop detecting element 1 consisting of a light emitting element 2 and a light receiving element 3 that are driven by the modulated signal of a drive circuit 4 and the output from the element 1 is integrated through a detection circuit 5. And the driving time interval of wiper blades 11 is set short by means of a processing circuit 9, provided that a difference between the previous time interval and a time required for reaching the first discrimination level from the previous drive is more than the prescribed value when an integral value 8 reaches the predetermined first discrimination level or more withing the previous time interval. Menswhile the abovementioned driving time interval is set long, if the integral value is below the second discrimination level smaller than the first one at the transient time for the previous time interval, so as to drive a wiper motor 10. Thus, a time interval for driving wiper blades can be adjusted to give comfortable feeling while preventing any wiping under dry condition.