The objective of the present invention is to provide a technique which enables analysis to be performed in real-time without taking a control or the like, by performing wavelet transformation at the same time, without pre-processing of a signal. The present invention provides a pain estimating method and device with which pain of an estimation target can be objectively and accurately estimated, and with which the quality and quantity thereof can be classified simply. The present invention provides a method for processing a signal of a target in response to a stimulus, and includes: a) a step of obtaining from the target a signal in response to a stimulus； (b) a step of subjecting the signal to cross correlation processing using part or all of the signal； and (c) a step of calculating a feature quantity of the signal and a coefficient correlated to the stimulus from the processing results obtained in b).
