A signal processing device according to the present invention is a signal processing device that processes data of a detected ultrasound waveform representing a temporal change in the intensity of ultrasound generated at a measurement position in a specimen and includes: a comparison unit that compares a predetermined standard ultrasound waveform and the detected ultrasound waveform at the measurement position and that calculates a degree of similarity between the predetermined standard ultrasound waveform and the detected ultrasound waveform; and a discrimination unit for discriminating whether or not the measurement position corresponds to a predetermined examination subject on the basis of the degree of similarity.