A radiography support device that supports imaging of an object with a radiation detection panel in which a plurality of pixels are two-dimensionally arranged and which detects radiation emitted from a radiation source, includes: a first reading control unit that reads first pixel signals from at least some of the plurality of pixels in a state in which the radiation is not emitted from the radiation source and a state in which the object is placed on the radiation detection panel; a first arithmetic unit that calculates a position of the object with respect to the radiation detection panel based on the first pixel signals; and a notification processing unit that performs a notification process in a case in which the position of the object is out of a predetermined range.