A subject extraction device (10) according to this disclosure comprises: a low resolution conversion unit (111) that generates a low resolution image by converting an image to low resolution; a subject candidate extraction unit (112) that extracts a subject region candidate from the low resolution image; a high resolution conversion unit (113) that converts to high resolution a boundary between the subject region and a non-subject region, makes a pixel-by-pixel determination as to whether the boundary is the non-subject region, and establishes the subject region and the non-subject region on the basis of the determination results; and a calculation resources allocation unit (114) that determines, as a first value, the value of calculation resources to be allocated to the subject candidate extraction unit (112) and, as a second value, the value of calculation resources to be allocated to the high resolution conversion unit (113), such that the maximum value of calculation resources available for use by the subject candidate extraction unit (112) and the high resolution conversion unit (113) will not be exceeded, and then allocates the calculation resources to the subject candidate extraction unit (112) and the high resolution conversion unit (113) on the basis of the first value and the second value that have been determined.