Disclosed is a screen synthesizing device which can achieve greater power saving effects when synthesizing a plurality of display screens containing moving images, without affecting the display result. In the disclosed device, a synthesis destination allocation determination unit (105) determines to synthesize the display layer which is the object of determination among the plurality of display layers including a first display layer having the first frame as a synthesis destination candidate and a second display layer having the second frame as a synthesis destination candidate, in either the first frame or the second frame on the basis of layout information which shows the positional relationship between the display layer which is the object of determination and a determination reference region which corresponds to the display layer which is the object of determination, and on the basis of the synthesis processing costs of the first frame and the second frame.