An image sensing device is disclosed. The image sensing device includes a plurality of unit pixels arranged as an array of unit pixels in a first direction and a second direction perpendicular to the first direction, and a device isolation structure wherein each of the unit pixels is disposed in a region isolated from adjacent unit pixels and includes a single photoelectric conversion element, a single floating diffusion region, and at least three transistors. The single photoelectric conversion element, the single floating diffusion region, and the at least three transistors are located in a region isolated by the device isolation structure.