To reduce a space and mix circulation time by mixing a first liq. with mixture of the first liq. and second liq. in piping.

To a mixer unit 10 for mixing chemical liqs., pure water is fed from a pure water feed hole 11 as a main liq., desired chemical liqs. are fed from respective chemical liq. feed holes 12-14. The same pure water as the main liq. is fed from a stirring pure water feed hole 15 for stirring the soln. with the flow of the pure water, thereby obtaining a uniform mixed liq. In pure water and chemical liq. pipings, flow rate control valves are mounted and flow-meters may be provided in the respective piping routes for confirming the flow rates, and he mixed soln. is fed from a mixed liq. outlet 16 via a valve to a processing bed to clean wafers. As a result, it is possible to make the uniform mixing in the pipe of a normal aperture used for pipings and reduce the space and mixing circulation time because a circulation mixing mechanism can be dispersed with.