A method of automatically tracking and photographing a celestial object, which moves relative to a photographic apparatus due to diurnal motion, in which, in order to photograph the celestial object, a trimming area that has been electronically trimmed from a part of an imaging area of an image sensor is moved while the celestial object is photographed, said method comprising: obtaining movement information of a celestial-object image on said imaging area; setting movement data for said trimming area based on the obtained said movement information of said celestial-object image; setting said trimming area and photographing time; and obtaining a photographing image at each trimming area while moving said trimming area based on the set said movement data of said trimming area, said trimming area, and said photographing time, wherein the photographing image at each trimming area is photographed at an exposure time of a movement period; wherein said setting of said trimming area and photographing time includes: cutting out said trimming area, which is smaller than said imaging area, from said imaging area of said image sensor; calculating a maximum photographing time in which said trimming area can be accommodated within said imaging area of said image sensor, when the said trimming area is virtually moved based on said movement data of said trimming area; and setting said maximum photographing time as a photographing time; said method further comprising: calculating the movement period of the trimming area; comparing the photographing time and the movement period of the trimming area; and when the photographing time is longer than the movement period, obtaining photographing image data per the movement period of the trimming area and setting a new photographing time by subtracting the movement period from the photographing time; wherein said movement period of said trimming area is set so that the movement distance of said celestial object image per the movement period in said trimming area is within a range so as not to exceed a pixel pitch of said trimming area. obtaining movement information of a celestial-object image on said imaging area; setting movement data for said trimming area based on the obtained said movement information of said celestial-object image; setting said trimming area and photographing time; and obtaining a photographing image at each trimming area while moving said trimming area based on the set said movement data of said trimming area, said trimming area, and said photographing time, wherein the photographing image at each trimming area is photographed at an exposure time of a movement period; wherein said setting of said trimming area and photographing time includes: cutting out said trimming area, which is smaller than said imaging area, from said imaging area of said image sensor; calculating a maximum photographing time in which said trimming area can be accommodated within said imaging area of said image sensor, when the said trimming area is virtually moved based on said movement data of said trimming area; and setting said maximum photographing time as a photographing time; said method further comprising: calculating the movement period of the trimming area; comparing the photographing time and the movement period of the trimming area; and when the photographing time is longer than the movement period, obtaining photographing image data per the movement period of the trimming area and setting a new photographing time by subtracting the movement period from the photographing time; wherein said movement period of said trimming area is set so that the movement distance of said celestial object image per the movement period in said trimming area is within a range so as not to exceed a pixel pitch of said trimming area. cutting out said trimming area, which is smaller than said imaging area, from said imaging area of said image sensor; calculating a maximum photographing time in which said trimming area can be accommodated within said imaging area of said image sensor, when the said trimming area is virtually moved based on said movement data of said trimming area; and setting said maximum photographing time as a photographing time; said method further comprising: calculating the movement period of the trimming area; comparing the photographing time and the movement period of the trimming area; and when the photographing time is longer than the movement period, obtaining photographing image data per the movement period of the trimming area and setting a new photographing time by subtracting the movement period from the photographing time; wherein said movement period of said trimming area is set so that the movement distance of said celestial object image per the movement period in said trimming area is within a range so as not to exceed a pixel pitch of said trimming area. calculating the movement period of the trimming area; comparing the photographing time and the movement period of the trimming area; and when the photographing time is longer than the movement period, obtaining photographing image data per the movement period of the trimming area and setting a new photographing time by subtracting the movement period from the photographing time; wherein said movement period of said trimming area is set so that the movement distance of said celestial object image per the movement period in said trimming area is within a range so as not to exceed a pixel pitch of said trimming area.