PROBLEM TO BE SOLVED: To extract a two-dimensional or three-dimensional object area with a simple operation in a short period of time from a plurality of two-dimensional tomographic images acquired by a medical image diagnostic device.SOLUTION: A control part 10 controls operations of a preprocessing part 20 and an image processing part 30, the preprocessing part 20 receives a designation input by a manual operation of an input part 40, acquires data of an object area and the approximate size thereof at the same time, and performs preprocessing for acquiring data of a non-object area, and the image processing part 30 generates a histogram of luminance data of a pixel of the object area and a histogram of luminance data of a pixel of the non-object area from the data of the object area and data showing the approximate size, and the data of the non-object area and data showing its approximate size acquired by the preprocessing part 20, approximates the respective histograms to a normal distribution, determines a threshold of area division by a Bays rule by using an approximate normal distribution of the object area and an approximate normal distribution of the non-object area, and extracts the object area and the non-object area.
