A hardness deriving device includes: an acquisition section configured to acquire plural ultrasound images obtained by ultrasound imaging a breast in a state in which the breast is pressed by a pressing member at a plurality of different pressures and a deriving section configured to find an amount of change at corresponding points between the plural ultrasound images acquired by the acquisition section, and to derive information indicating a hardness of tissue of the breast based on the amount of change at the corresponding points.
