The diagnostic support apparatus includes a feature quantity calculation unit vectorizing a test image into shift-invariant feature quantities, a base representation unit transforming the shift-invariant feature quantities of the test image into a linear combination of base vectors with first coefficients, the base vectors being calculated from a plurality of vectors representing shift-invariant feature quantities of a plurality of normal structural images including no lesion site, a lesion determination unit determining that the test image includes a lesion site when a difference between the first coefficients and second coefficients is greater than a determination threshold value, the second coefficients being used to transform shift-invariant feature quantities calculated from one of the normal structural images into a linear combination of the base vectors, and an output unit outputting a result of the determination by the lesion determination unit.