To provide an optical raindrop sensor for eliminating a drift effect after power is turned on.

The optical raindrop sensor is provided with a constitution for closely bringing a glass plate into contact with an optical system for controlling a light emitting element 4, a light receiving element 5 and a light emitting/receiving optical path through a transmissive sheet, and controlling a drive current of the light emitting element 4 so as to maintain a fixed signal level of the received light. The drift correcting method of the optical raindrop sensor is characterized by correcting the signal level of the received light against the drift by coefficients of a map preset by the drive current of the light emitting element 4 after power is turned on.