A focusing device comprises: an image capturing unit that captures a subject image formed via an optical system including a lens for executing focus adjustment and outputs an output signal; an edge detection unit that detects an edge signal among the output signal in correspondence to each color component among a plurality of color components contained in an image based upon the output signal; a calculation unit that calculates edge differential values each of which is a differential value of the edge signal in correspondence to the each color component; and a control unit that controls a moving direction along which the lens is to move based upon a comparison of the edge differential values.