PROBLEM TO BE SOLVED: To obtain an accurate position and volume of a myocardial infarction region and thus to improve accuracy of image diagnosis by extracting an accurate myocardial infarction region inside a cardiac muscle region from an image including the heart in an image processor.SOLUTION: An image processor 10 has: positioning means 43 for positioning images of a plurality of time phases including the heart； outer wall extraction means 44 for extracting the outer wall of the heart on the basis of an image of at least one of the plurality of time phases； transition coefficient arithmetic means 45a for obtaining a transition coefficient of a signal value inside the extracted outer wall on the basis of images of the plurality of time phases； and myocardial infarction region extract means 45c and lumen area extraction means 45d which separate the myocardial infarction region and a lumen area and extract them respectively by performing threshold processing of the transition coefficient.
