1. An image capturing apparatus comprising: an image capturing unit configured to photoelectrically convert an object image formed by an image capturing optical system; a moving unit configured to move the object image relative to the image capturing unit; a camera shake detection unit configured to detect a camera shake; a calculation unit configured to calculate a moving amount of the moving unit to cancel the camera shake on the basis of an output from the camera shake detection unit; a driving unit configured to drive the moving unit by adding a predetermined offset amount to based on the moving amount calculated by the calculation unit; and a control unit configured to acquire a plurality of captured images while changing the moving said moving unit by said driving unit by adding a predetermined offset amount to the moving amount; a foreign substance detection unit configured to detect foreign substance area information including at least position information about a foreign substance adhered near said image capturing unit by comparing the plurality of captured images based on the offset amount; an image correction unit configured to correct the foreign substance area in the plurality of captured images based on a detection result of said foreign substance detection unit and the offset amount; and an image composition unit configured to composite the plurality of captured images based on the offset amount and the moving amount.