An optical image measurement device comprising: a light source configured to emit a low-coherence light; an interference-light generator (162,163,164,174) configured to generate an interference light by splitting the emitted low-coherence light into a signal light heading toward a measurement subject and a reference light heading toward a reference object, and superimposing the signal light passed through the measurement subject and the reference light passed through the reference object; a changer configured to change a difference in optical path length between the signal light and the reference light; a detector configured to detect the generated interference light; and an image forming part configured to form an image based on the result of the detection by the detector; characterized in that the optical image measurement device further comprises: an analyzer configured to analyze the formed image to calculate either a signal level of the image or a ratio of a signal level of the image to a noise level of the same image, and determine whether the signal level or the ratio of the signal level to the noise level exceeds a threshold value; and a controller configured to control the changer to change the difference in optical path length so that the analyzer determines the signal level or the ratio to exceed the threshold value, wherein the image forming part is configured to form an image within a predetermined frame; the controller is configured to control to change the difference in optical path length so that a partial image corresponding to a predetermined depth position of the measurement subject in the image determined by the analyzer to exceed the threshold value is placed in a specific position within the predetermined frame, the analyzer is configured to analyze the image determined by the analyzer to exceed the threshold value, to find a position of the partial image within the predetermined frame, and to calculate displacement between the found position and the specific position; and the controller is configured to control to change the difference in optical path length by a distance corresponding to the displacement, thereby placing the partial image in the specific position. a light source configured to emit a low-coherence light; an interference-light generator (162,163,164,174) configured to generate an interference light by splitting the emitted low-coherence light into a signal light heading toward a measurement subject and a reference light heading toward a reference object, and superimposing the signal light passed through the measurement subject and the reference light passed through the reference object; a changer configured to change a difference in optical path length between the signal light and the reference light; a detector configured to detect the generated interference light; and an image forming part configured to form an image based on the result of the detection by the detector; characterized in that the optical image measurement device further comprises: an analyzer configured to analyze the formed image to calculate either a signal level of the image or a ratio of a signal level of the image to a noise level of the same image, and determine whether the signal level or the ratio of the signal level to the noise level exceeds a threshold value; and a controller configured to control the changer to change the difference in optical path length so that the analyzer determines the signal level or the ratio to exceed the threshold value, an analyzer configured to analyze the formed image to calculate either a signal level of the image or a ratio of a signal level of the image to a noise level of the same image, and determine whether the signal level or the ratio of the signal level to the noise level exceeds a threshold value; and a controller configured to control the changer to change the difference in optical path length so that the analyzer determines the signal level or the ratio to exceed the threshold value, wherein the image forming part is configured to form an image within a predetermined frame; the controller is configured to control to change the difference in optical path length so that a partial image corresponding to a predetermined depth position of the measurement subject in the image determined by the analyzer to exceed the threshold value is placed in a specific position within the predetermined frame, the analyzer is configured to analyze the image determined by the analyzer to exceed the threshold value, to find a position of the partial image within the predetermined frame, and to calculate displacement between the found position and the specific position; and the controller is configured to control to change the difference in optical path length by a distance corresponding to the displacement, thereby placing the partial image in the specific position.