To provide water filling control technology to more exactly decide an evaporation amount in course of stopping the operation of a developing device without requiring measurement of liquid temperature and ambient temperature in course of stopping the operation thereof.

The water filling control method is prepared for a developing device equipped with a plurality of processing tanks 21 and a water filling tank 23 storing water to be supplied to the processing tanks in a developing part for performing development processing of applied photosensitive material. The predicted evaporation amount per time decided from temperature of a processing solution when stopping the operation of the developing device and temperature of the processing solution when restarting the operation thereof, and regulated in accordance with a rate of change of the liquid temperature with lapse of time of the processing solution in course of stopping the operation of the developing device is decided. Furthermore, a water filling amount for the processing tank is decided based on the decided predicted evaporation amount and elapsed time of stopping the operation.