PROBLEM TO BE SOLVED: To stably take in data by determining a timing of taking in data in wavelength sweeping by a trigger signal generated in the wavelength sweeping.SOLUTION: An optical coherence tomographic image forming apparatus for forming a tomographic image based on interference light between measurement light and reference light includes: a converter for converting the light intensity of the interference light into an electric digital signal at a sampling timing an optical detector for generating a trigger signal by detecting light with a preset and prescribed wavelength in a single wavelength sweeping of a light source and a delay section for delaying a digital signal that has been output from the converter at each sampling timing by a prescribed delay time and outputting it. A signal processing section generates one line of line data using a digital signal for a prescribed period from a time when the trigger signal has been generated in the optical detector, out of digital signals output from the delay section.
