An image sensing device includes a Bayer pixel group configured include pixels that form a Bayer pattern and are arranged in a 2×2 matrix, a 4SUM pixel group configured to include pixels that correspond to the same colors and are arranged in a 2×2 matrix, a Bayer floating diffusion disposed at a center portion of the Bayer pixel group, a 4SUM floating diffusion (FD) region disposed at a center portion of the 4SUM pixel group, a sensing node, and a gain conversion transistor coupled between the sensing node and any one of the Bayer floating diffusion (FD) region and the 4SUM floating diffusion (FD) region.