The present invention relates to a method for automatically discriminating a control solution from a sample in a measurement system for measuring a target ingredient in the sample by using a measurement wavelength and a reference wavelength, wherein as the control solution, a control solution having a response value lower than a lower limit value (threshold) of a response value, such as absorbance, supposed when luminance of the sample is measured at the reference wavelength and having a response value higher than an upper limit value (threshold) of a response value supposed when luminance of the sample is measured at the detection wavelength for detecting whether the sample is supplied is used.