1. An imaging device, comprising: an imaging lens; an image pickup element in which color filters with a prescribed color filter array are arranged on multiple pixels including photoelectric conversion elements arranged in a first direction and a second direction perpendicular to the first direction, the image pickup element including first and second phase difference pixels on which a subject image having passed through different first and second areas of the imaging lens is pupil-divided and image-formed; a color image acquisition device which performs thinning-reading pixel signals according to a thinning pattern from the image pickup element, or extracting pixel signals according to the thinning pattern from a color image that is read from the image pickup element and corresponds to the prescribed color filter array, and acquiring a thinned color image; a moving image generating device which generates moving image data, based on the thinned color image; a phase difference detection device which detects a phase difference between output signals that correspond to the first and second phase difference pixels included in the thinned color image, based on each output signal; and a focus adjustment device which adjusts a focus position of the imaging lens based on the phase difference detected by the phase difference detection device, wherein the prescribed color filter array includes first filters corresponding to at least one first color, and second filters corresponding to at least two second colors having lower contribution ratios for acquiring luminance signals than the first color has, and has a basic array pattern according to which the first filters and the second filters are arranged, the basic array pattern being repeatedly arranged in the first direction and the second direction, at least one of each of the first filters and the second filters corresponding to the respective second colors is arranged on each of pixel lines in the first direction and the second direction in the basic array pattern, and the first and second phase difference pixels are arranged at positions of the filters having the same color on pixel lines in the first direction, on the thinning pattern in the focal point detection area of the image pickup element, wherein in the thinned color image, pixels having a color identical to a color of pixels at positions of the first and second phase difference pixels are arranged, in at least one of the first and second directions, adjacent to the first and second phase difference pixels, the device further comprises an interpolating calculation device which calculates pixel values of the pixels at the positions of the first and second phase difference pixels in the thinned color image by interpolating pixel values of surrounding pixels including pixels having a same color adjacent to the first and the second phase difference pixels, and the moving image generating device generates the moving image data based on a color image using values calculated by the interpolating calculation device as pixel values of pixels at positions of the first and second phase difference pixels in the thinned color image.