1. A quality control method for an analysis supporting liquid in an automatic analyzing apparatus which includes, to perform an analysis on a specimen, a specimen dispensing unit which dispenses the specimen by using, as a pressure transmitting medium, an analysis supporting liquid including purified water and serving to support the analysis on the specimen, a reagent dispensing unit which dispenses a reagent by using the analysis supporting liquid as the pressure transmitting medium, a cleaning unit which cleans, by using the analysis supporting liquid as a cleaning liquid, a reaction vessel in which the specimen and the reagent are mixed and made react to each other, and a diluted solution dispensing unit which dispenses a diluted solution including the analysis supporting liquid, and which controls a quality of the analysis supporting liquid, the quality control method comprising: dispensing the analysis supporting liquid into the reaction vessel by one of the specimen dispensing unit, the reagent dispensing unit, the cleaning unit, and the diluted solution dispensing unit; performing an optical measurement with respect to a liquid, including the analysis supporting liquid dispensed in the dispensing, in the reaction vessel; generating analysis data of the analysis supporting liquid by using a result measured in the performing the optical measurement; and determining the quality of the analysis supporting liquid by comparing the analysis data generated in the data generating with reference data.