PROBLEM TO BE SOLVED: To provide an image processing technology for stably improving extraction accuracy at a high speed when extracting an object area from a moving image.SOLUTION: An image processing device 3 includes: a shape model fitting part 120 for determining a fitting function for approximating a boundary of a lung field area on a frame image by performing fitting processing for fitting a shape model representing a general shape of the lung field area of the frame image, and sequentially acquiring lung field area boundary information obtained by reflecting at least the fitting function and a shape model control part 130 for performing shape model change processing for sequentially changing a shape model used in the fitting processing to the frame image along a time direction. A fitting function F is composed of the prescribed number of functions, and a shape model M is a model for determining the fitting function F, and includes at least one piece of information in the prescribed number and the allowable range of a degree of each of the functions.
