A skin diagnostic device includes an image acquisition unit that acquires a skin image obtained by capturing skin, an image analyzer that calculates an index value indicating a darkness level of a color of a discolored region of the skin from the obtained skin image, a threshold determination unit that determines a threshold based on the calculated index value and a size of a contrast of the skin image, and a skin diagnostic unit that performs a diagnosis on the skin by comparing the determined threshold and normalized luminance value data obtained by normalizing luminance value data of the skin image with an average luminance value of the luminance value data.
