An imaging device includes a pixel array with first and second pixels respectively having first and second conversion gains connected to row and column lines; a row driver determining a selection row line among the row lines; a readout circuit obtaining first and second pixel signals from first and second pixels connected to the selection row line; a column driver generating first and second image data from the first and second pixel signals; and an image signal processor using the first and second image data to generate an object image. The second pixels include an expansion capacitor connected between a floating diffusion node and a ground node. Exposure time of the first pixels is equal to or longer than exposure time of the second pixels. An area of a light receiving region of the first pixels is equal to an area of a light receiving region of the second pixels.