A diagnostic support apparatus includes a base vector matching unit configured to match test image base vectors used for a base representation of a test image feature quantity of a test image and normal image base vectors used for a base representation of a normal image feature quantity of a normal image, a lesion determination unit configured to determine that the test image includes an image of a lesion site when a difference between a test image base coefficient and a normal image base coefficient is greater than a threshold, the test image base coefficient being a coefficient with which the test feature quantity is transformed to the base representation, and the normal image base coefficient being a coefficient with which the normal feature quantity is transformed to the base representation, and a determination result output unit configured to output a result of the determination by the lesion determination unit.