A signal processing apparatus scans a beam of elastic waves into an object to be examined, acquires received waveform data of a plurality of scan lines, and performs signal processing to form a tomographic image of said object to be examined from the received waveform data of the plurality of scan lines. The signal processing apparatus includes a scan line correlation calculation part (009) that calculates a correlation value of received waveform data between a first scan line and a second scan line that has a prescribed correlation with the first scan line, for a plurality of positions on the scan lines, and a correlation change position extraction part (010) that extracts, from among the plurality of positions on said scan lines, a position at which the correlation value becomes a value different from a prescribed value as a position at which a unique region can exist.
