To practically constitute a developing apparatus capable of carrying out satisfactorily stable processing without increasing the number of stable processing tanks and the capacity thereof.

A stable processing system of successively sending a developed printing paper to four stable processing tanks, and then, carrying out the processing while dipping the paper in the processing liquid stored in each tank is formed. Among sub tanks 25A, 25B, 25C and 25D for the stable processing tanks, the stable processing liquid (STB) is replenished to the sub tank 25D positioned on the downmost stream side in the printing paper conveying direction, and also, alkali ion water (AW) is supplied from an alkali ion water generating apparatus 51, and the processing liquid mixed with the liquid (STB) and the water (AW) is discharged to a waste liquid tank 56 while making the processing liquid overflow the tank 25A first, positioned on the upstream side in the conveying direction of the printing paper P.