An optical imaging apparatus for diagnosis generates a closed curve which precisely reproduces the shape of the indwelled stent and the shape of the inner wall of the biological tissue at the indwelling position of the stent. The optical imaging apparatus analyzes intensity change in transmission direction of the light from the transmission and reception unit for every one of the respective line data； based on the result of the analysis detects pixel data expressing the stent position in the transmission direction； labels each pixel data expressing the detected stent position； eliminates, within the respective labeling groups applied with the same labels, labeling groups in each of which the number of pixel data in the circumferential direction is a predetermined value or less； calculates center position for each labeling group not eliminated； and generates a stent closed-curve using the center position of each labeling group.
