This invention provides an apparatus such as a focus adjustment apparatus capable appropriately adjusting focusing in accordance with chromatic aberration, a control method therefor, and a medium such as a storage medium for supplying a control program therefor. An apparatus such as a focus adjustment apparatus which forms a plurality of color component signals corresponding to predetermined different color components of object light received through an optical system, and forms a signal for focus adjustment on the basis of a signal formed by changing a ratio of the plurality of color component signals formed, a control-method therefor, and a medium such as a storage medium for supplying a control program therefor are provided.