Abstract: The concentration of a developer for use in developing resists in the fabrication of integrated circuits of semiconductors is adjusted highly accurately using a load cell. A stock developer and pure water are supplied to a mixing tank supported on a load cell, and mixed into a diluted developer in the mixing tank. The concentration of the diluted developer from the mixing tank is analyzed by an automatic analyzer, which then calculates the weight of a stock developer or pure water to be introduced into the mixing tank based on the analyzed concentration in order to achieve a predetermined concentration. Then, either a stock developer or pure water of the calculated weight is supplied to the mixing tank until the weight, as measured by the load cell, of the mixing tank containing the stock developer and the pure water is increased by the calculated weight. Thereafter, the diluted developer is transferred from the mixing tank to a reservoir tank, while both tanks are maintained under a nitrogen gas atmosphere.