[Problem] To suppress discomfort associated with transition of a mode when images obtained from a plurality of imaging elements are synthesized. [Solution] The present disclosure provides an image processing device comprising: a synthesis processing unit which synthesizes a plurality of pieces of image information obtained from a plurality of imaging elements for capturing images of the same object; and a synthesis mode determination unit which determines a mode of the synthesizing in accordance with a predetermined variable value and in which a threshold value of the variable for determining the mode is set in accordance with a plurality of modes.