To efficiently improve the image quality of a tomographic image without lowering its effect by phase shift when processing using a plurality of coherence signal data obtained by OCT measurement in SS-OCT.

The coherence signal processing method in an optical tomographic image apparatus using an SS-OCT measuring method is characterized by performing phase correcting processing for correcting the phase shift of a plurality of coherence signals obtained by measuring the same measuring region of a measuring target a plurality of times, further characterized by performing averaging processing before Fourier transform after the phase correcting processing is performed, and furthermore characterized by adapting a Doppler system after the phase correcting processing is performed.