By making use of a set of loading of stimulation and no loading, variation signals in time of hemoglobin density at a plurality of measurement points of a subject attached of an optical measurement probe and corresponding to a plurality of channels are detected, and for the respective detected hemoglobin variation signals principal component analysis is performed as well as a representative signal having a higher contribution rate is extracted and the extracted representative signal is displayed on a monitor. A correlation between the representative signal and a task reference and response waveform representing a response pattern of a living body in response to a stimulation task is calculated, and a representative signal having the highest correlation value as calculated is displayed in a discriminable manner from the other signals as a task related signal which responds most to the stimulation given to the subject. From weights of the respective channels for the representative signal displayed as the task related signal, an optical measurement point or region, which responds most to the task is identified and displayed in discriminable manner.