1. An image sensing apparatus comprising: an image sensing device that has a plurality of pixels; a smoothing unit that smoothes a dark image signal acquired with said image sensing device shielded from light and generates a corrected dark image signal; a dark correction unit that performs dark correction on an object image signal acquired by sensing an object by said image sensing device by subtracting the corrected dark image signal from the object image signal; an extraction unit that extracts, as a defective pixel of said image sensing device, a pixel of which an obtained difference is outside a preset range by subtracting the smoothed corrected dark image signal from the dark image signal; and a defective pixel correction unit that corrects an image signal output from the defective pixel using an image signal output from a pixel peripheral to the defective pixel.