1. An imaging apparatus comprising: a tomogram generating unit which successively generates a tomogram regarding each of a plurality of tomographic planes arrayed in different positions in a three-dimensional area of a subject; a projected image generating unit which generates a projected image by executing projection processing of a specific value of pixels in the tomogram generated by said tomogram generating unit for each of a plurality of tomographic planes arranged in the direction in which said tomographic planes are arrayed; and a synthesized image generating unit which generates a plurality of synthesized images by synthesizing said tomograms generated by said tomogram generating unit with a projected image generated by said projected image generating unit, wherein: said projected image generating unit is configured to end projection processing when the specific value of a pixel reaches a second threshold after the specific value of the pixel reaches a first threshold in the direction in which said tomographic planes are arrayed; and said synthesized image generating unit so synthesizes each of the tomograms with the projected image that the positions of pixels of said tomograms generated by said tomogram generating unit in the direction in which said tomographic planes are arrayed and the positions of pixels projected in the direction in which said tomographic planes are arrayed when said projected image generating unit executes said projection processing match each other in said three-dimensional area.