An estimation device includes at least one processor, in which the processor functions as a learned neural network that derives a result of estimation relating to a bone density of a bone part from a simple radiation image acquired by simply imaging a subject including the bone part or a DXA scanning image acquired by imaging the subject by a DXA method. The learned neural network is learned by using, as teacher data, a composite two-dimensional image representing the subject, which is derived by combining a three-dimensional CT image of the subject, and information relating to the bone density of the subject.