1. A fundus camera comprising: an illumination unit configured to illuminate an ocular fundus of a subject's eye; an autofluorescent exciter filter configured to be insertable into and retractable from an illumination optical path of the illumination unit; an observation and photographing unit configured to receive reflection light from the ocular fundus illuminated by the illumination unit and form an ocular fundus image; an autofluorescent barrier filter configured to be insertable into and retractable from an observation and photographing optical path of the observation and photographing unit; an image capturing unit configured to capture an ocular fundus image formed by the observation and photographing unit; and a calculation unit configured to calculate image data from the image capturing unit; wherein the calculation unit of the fundus camera which can perform both of color image photographing and photofluorography, converts the ocular fundus image which is illuminated using the autofluorescent exciter filter inserted into the illumination unit and captured by a color image capturing unit as a color image, in a state that no autofluorescent barrier filter is inserted into the observation and photographing unit, into a monochromatic image from specific color data of the color image, wherein the calculation unit converts the color image including R, G and B color data into monochromatic image data using G color data, wherein the calculation unit converts the image data into monochromatic image data based on two color data of R color data, G color data, and B color data, wherein a selection unit is configured to select a first mode in which the barrier filter is retracted from the light path and a generation unit generates a color image by using the data, and a second mode in which the exciter filter is arranged in the light path and the calculation unit generates monochromic image data by using a specific component of the color data, and wherein the calculation unit is configured to generate a monochromatic image based on an image with a reduced value of a pixel in the second mode in a case where an R/G value is larger than a threshold value, with respect to values of R, G and B components of each pixel in the image data.