Abstract: A method for obtaining image data of a subject, including; a first scanning step including a plurality of steps W, each step W being a step of determining one place existing in a one-dimensional, two-dimensional, or three-dimensional first space; and a second scanning step of scanning insides of second spaces including at least one of the places, wherein the second scanning step includes a step X of randomly determining a location of an observation point and a step Y of obtaining a piece of image data for the observation point, and, at a time point of end of scanning an inside of one of the second spaces, the second space has a first region including 50% of observation points and a second region existing outside the first region and including remaining 50% of the observation points, the second region being larger than the first region by at least 15%.