1. A medical decision making support apparatus comprising: an inference unit configured to obtain an inference result by performing inference processing associated with a medical diagnosis based on a plurality of pieces of input medical information; a calculation unit configured to calculate a degree effect on the inference result in association with at least one element of the input medical information that affects an inference probability for the inference result; a selection unit configured to select at least one calculated element which reduces the inference probability for the inference result; and a presentation unit configured to present the selected at least one element as negative information, wherein the degree effect on the inference result, calculated by the calculation unit, is further in association with each of a plurality of partial sets including medical information extracted from the plurality of pieces of medical information as an element.