An optical imaging diagnostic apparatus including: a designating unit for designating a predetermined circumferential-direction position at the circumference of the transmitting and receiving unit on the cross-sectional image displayed; an extraction unit for extracting, within the plurality of line data used for the generation of the cross-sectional image, line data corresponding to circumferential-direction position designated in the designating unit from the storage unit; a calculation unit for calculating attenuation rate in a predetermined region in a radial direction of a body lumen with respect to the extracted line data; and a display unit for displaying the calculated attenuation rate.