An imaging apparatus having imaging means including a plurality of pixels for photoelectrically converting an optical image of an object formed by a photographing optical system including a photographing lens, for generating pixel data by using outputs of the plurality of pixels, comprising: pupil division means constructed by a microlens array in which microlenses are two-dimensionally arranged; exposure condition determination means for determining an exposure condition of the imaging means on the basis of pixel data which is generated by photoelectrically converting, by the plurality of pixels, rays of light which enter through the pupil division means; and vignetting determination means for obtaining information about actual photographing conditions of the imaging apparatus and determining a vignetting of a pixel among the plurality of pixels caused by the photographing optical system on the basis of the obtained information and information about a construction of the photographing optical system, characterized in that predetermined pixels (21-a, 21-b, 21-c, 21-d, 21-e) among the plurality of pixels of the imaging means are arranged in correspondence to each microlens and each pixel of the predetermined pixels corresponding to one of the microlenses is arranged so as to be conjugate by that microlens with an exit pupil area (25-a, 25-b, 25-c, 25-d, 25-e) on an exit pupil plane of the photographing lens; and the exposure condition determination means is adapted to determine the exposure condition of the imaging means for a first exposure mode on the basis of pixel data generated from pixels among the predetermined pixels corresponding to each microlens that have, in accordance with the vignetting determined by the vignetting determination means, the least vignetting, and for a second exposure mode (S304, S307) on the basis of data obtained by adding pixel data generated from the predetermined pixels (641a, 641b, 641c) corresponding to each microlens. pupil division means constructed by a microlens array in which microlenses are two-dimensionally arranged; exposure condition determination means for determining an exposure condition of the imaging means on the basis of pixel data which is generated by photoelectrically converting, by the plurality of pixels, rays of light which enter through the pupil division means; and vignetting determination means for obtaining information about actual photographing conditions of the imaging apparatus and determining a vignetting of a pixel among the plurality of pixels caused by the photographing optical system on the basis of the obtained information and information about a construction of the photographing optical system, characterized in that predetermined pixels (21-a, 21-b, 21-c, 21-d, 21-e) among the plurality of pixels of the imaging means are arranged in correspondence to each microlens and each pixel of the predetermined pixels corresponding to one of the microlenses is arranged so as to be conjugate by that microlens with an exit pupil area (25-a, 25-b, 25-c, 25-d, 25-e) on an exit pupil plane of the photographing lens; and the exposure condition determination means is adapted to determine the exposure condition of the imaging means for a first exposure mode on the basis of pixel data generated from pixels among the predetermined pixels corresponding to each microlens that have, in accordance with the vignetting determined by the vignetting determination means, the least vignetting, and for a second exposure mode (S304, S307) on the basis of data obtained by adding pixel data generated from the predetermined pixels (641a, 641b, 641c) corresponding to each microlens. for a first exposure mode on the basis of pixel data generated from pixels among the predetermined pixels corresponding to each microlens that have, in accordance with the vignetting determined by the vignetting determination means, the least vignetting, and for a second exposure mode (S304, S307) on the basis of data obtained by adding pixel data generated from the predetermined pixels (641a, 641b, 641c) corresponding to each microlens.