1. An imaging apparatus, comprising: a supporting plate which supports a sample; a light source which irradiates light onto an imaging target area on the supporting plate; an imaging unit on which a plurality of image sensors having a light receiving area respectively are discretely disposed on an image plane two-dimensionally in an X direction and a Y direction; an imaging optical system which guides light from the imaging target area and forms an imaging target area image corresponding to the imaging target area on the imaging plane of the imaging unit; a moving unit which relatively moves the imaging target area image and the plurality of image sensors in the Y direction in order to perform a plurality of times of imaging for the imaging target area image while changing a position of an imaging area of each of the image sensors; and a merging unit which merges images of imaging areas acquired by the plurality of times of imaging and generates an image of the entire imaging target area, wherein a size of an effective field of view of the imaging optical system is larger than a size of the imaging target area image, when x 1 is a length in the X direction and y 1 is a length in the Y direction of the imaging target area image, x 2 is a length in the X direction and y 2 is a length in the Y direction of the image sensor, and x 3 is a length in the X direction and y 3 is a length in the Y direction of the light receiving area, 1.5<x 2 /x 3 <2.0, 1.5<y 2 /y 3 <2.0, and x 3 ≧x 1 /m (m is 3 or greater odd number) are satisfied, the plurality of image sensors are arranged so that odd rows and even rows are alternately disposed in the Y direction at a pitch not less than y 2 and not greater than 2*y 3 , each of the odd rows being constituted by (m−1)/2 number of image sensors lined up in the X direction at 2*1/m pitch, each of the even rows being constituted by (m+1)/2 number of image sensors lined up in the X direction at 2*1/m pitch with a 1/2 phase shift with respect to the odd row, and the length in the Y direction of an area covering light receiving areas of the image sensors on the first row to the light receiving areas of the image sensors on the last row is longer than the length y 1 in the Y direction of the imaging target area image.