PURPOSE: To reduce a frequency of dry wiping of a wiper so as to prevent an offensive sight for a driver by elongating an integral time by a specified time when an integrated value of output of a rain drop sensor is smaller than a second threshold value.

CONSTITUTION: When rain drop pulses input from a rain drop sensor 10 are integrated and the integrated value thereof is over a threshold value R1, it is judged that whether a timer value at the point when an integrated value R exceeded over the threshold value R1 is less than a mode up judging time set for every respective modes or not. When it is under the judging time, mode up is made to perform, and when it is larger than the judging time, mode holding process is made to perform, in a microcomputer 1. Moreover, when the integrated value R is less than 1/8.R1 as a second threshold value, an interval time is elongated by a specified time. Meanwhile in the case where integrated value R is small due to omission of detection on the rain drop sensor 10, the mode corresponding to this time interval is kept, when the integrated value R increases to reach over 1/2.R1 as a third threshold value before the specified time elapses.