In order to achieve a prediction approximating an actual change with time of a pixel value in a tissue with higher accuracy, provided is a simulator, which is configured to predict a change with time of a pixel value in a tissue of an object, including: an object information acquisition unit configured to acquire information on the object; a protocol acquisition unit configured to acquire an injection protocol for a contrast medium; a tissue information acquisition unit configured to acquire information on the tissue; and a prediction unit configured to predict, based on the information on the object, the injection protocol, and the information on the tissue, a change with time of a pixel value of each of a plurality of compartments obtained by dividing the tissue along a blood flow direction.