To precisely weight and fill an alkali agent and to ensure satisfactory stable photographic performance when a developing soln. is prepd. and processing is carried out by measuring the amt. of the alkali agent charged into a vessel while filling the alkali agent having a specified average diameter and filling the alkali agent into the vessel up to a position corresponding to a specified percentage of the entire lower part of the vessel.

Chemicals such as a solid granular alkali agent and a developing agent are successively introduced into a vessel and plural chemical layers are formed or the layers are further mixed by applying vibration to obtain a solid developer. In this case, the average diameter of the alkali agent is 0.5-2.0mm, the amt. of the alkali agent charged into the vessel is measured while filling the alkali agent and the alkali agent is filled into the vessel up to a position corresponding to 40% preferably 25% of the entire lower part of the vessel. The alkali agent is especially preferably charged into the bottom layer of the vessel. The weighting precision of the alkali agent is enhanced.