1. An imaging apparatus comprising: a first imaging unit including (1) a system of one or more lenses defining an optical axis and (2) an image pickup unit, the first imaging unit capturing a visual field all around the optical axis of the first imaging unit and generating image data of the captured visual field as omnidirectional image data, wherein the omnidirectional image data forms an annular shape; a second imaging unit including (1) a system of one or more lenses defining an optical axis orthogonal to the optical axis of the first imaging unit and (2) an image pickup unit, wherein the first imaging unit is positioned outside of any angle of view of the second imaging unit, the first imaging unit is configured to capture the image in both of a front direction and a back direction with respect to the imaging apparatus, the front and back directions being parallel to the optical axis of the second imaging unit, the first imaging unit has a vertical angle of view in the front direction, the vertical angle of view in the front direction including a depression angle of 20 degrees towards the optical axis of the second imaging unit, and the first imaging unit has a vertical angle of view in the back direction, the vertical angle of view in the back direction including a depression angle of 20 degrees towards the optical axis of the second imaging unit; an image converter that converts at least a part of the omnidirectional image data, which is generated by the first imaging unit, to image data having a rectangular display area and thereby generates conversion image data; a display unit that displays an image corresponding to the conversion image data, which is generated by the image converter; and an image synthesizer that synthesizes area image data, which is generated by the second imaging unit, and the conversion image data, which is generated by the image converter, and thereby generates synthesis image data, wherein the display unit displays an image corresponding to the synthesis image data.