A data processing method of reducing signals to numerical values and processing the numerical values are provided. The signals are obtained by using a probe array where probes of a plurality of kinds are immobilized on a solid phase as so many spots such that a plurality of spots of probes of one kind are arranged on the solid phase and causing the array to react with a target substance. The method comprises (1) a step of acquiring the signal from each spot as numerical data, and (2) a step of eliminating singular values from the numerical data obtained for the plurality of spots of probes of one kind and processing the remaining numerical data to determine representative numerical data.