An imaging device comprising: a plurality of pixels, each including a photoelectric conversion unit, a floating diffusion configured to hold charge generated in the photoelectric conversion unit, an amplifier transistor electrically connected to the floating diffusion, and a capacitor including an electrode, the capacitor being disposed so that electrical connection of the capacitor to the floating diffusion is switchable in accordance with a signal supplied to the electrode, wherein the electrical connection of the capacitor to the floating diffusion is switched to vary a capacitance value of an input node of the amplifier transistor, wherein each of the plurality of pixels has an active region (313A, 313B) including a first region and a second region, the first region and the second region being arranged with the electrode therebetween in plan view, wherein a portion that is a portion of the active region (313A, 313B) and that is located under the electrode forms at least a portion of the capacitor, wherein the first region includes a first semiconductor region of a first conductivity type, the first semiconductor region forming at least a portion of the floating diffusion, wherein the second region includes a second semiconductor region (312, 405, 505, 605, 705, 805, 905) of a second conductivity type opposite to the first conductivity type, wherein an insulating film is disposed on the second semiconductor region (312, 405, 505, 605, 705, 805, 905), and wherein the second semiconductor region forms an interface with an insulator isolation portion, characterized in that at least a part of the second region does not overlap the electrode and in that the insulator isolation portion is provided on the side of the second region opposite the electrode. a plurality of pixels, each including a photoelectric conversion unit, a floating diffusion configured to hold charge generated in the photoelectric conversion unit, an amplifier transistor electrically connected to the floating diffusion, and a capacitor including an electrode, the capacitor being disposed so that electrical connection of the capacitor to the floating diffusion is switchable in accordance with a signal supplied to the electrode, a photoelectric conversion unit, a floating diffusion configured to hold charge generated in the photoelectric conversion unit, an amplifier transistor electrically connected to the floating diffusion, and a capacitor including an electrode, the capacitor being disposed so that electrical connection of the capacitor to the floating diffusion is switchable in accordance with a signal supplied to the electrode, wherein the electrical connection of the capacitor to the floating diffusion is switched to vary a capacitance value of an input node of the amplifier transistor, wherein each of the plurality of pixels has an active region (313A, 313B) including a first region and a second region, the first region and the second region being arranged with the electrode therebetween in plan view, wherein a portion that is a portion of the active region (313A, 313B) and that is located under the electrode forms at least a portion of the capacitor, wherein the first region includes a first semiconductor region of a first conductivity type, the first semiconductor region forming at least a portion of the floating diffusion, wherein the second region includes a second semiconductor region (312, 405, 505, 605, 705, 805, 905) of a second conductivity type opposite to the first conductivity type, wherein an insulating film is disposed on the second semiconductor region (312, 405, 505, 605, 705, 805, 905), and wherein the second semiconductor region forms an interface with an insulator isolation portion, characterized in that at least a part of the second region does not overlap the electrode and in that the insulator isolation portion is provided on the side of the second region opposite the electrode.