The image merge device includes a common area determination unit configured to determine a common area between a first image and a second image; a correlation calculation unit configured to calculate a correlation level indicating a degree of a gap between the first image near a boundary of the first image and the second image and the second image near the boundary when the first image and the second image are aligned using the common area; and a superimposed area determination unit configured to determine a superimposed area in which the first and second images are superimposed near the boundary based on the correlation level calculated by the correlation calculation unit.