To provide an interchangeable lens camera system for shooting with the best in-focus position, no matter how a group of two or more interchangeable lenses to produce different degrees of spherical aberrations and a group of cameras of different types with different evaluated autofocus frequencies are combined. The camera system of this invention includes a lens unit and a camera body to be removable and attachable from/to each other. The lens unit includes a first computing section for acquiring shooting parameters during a focusing operation and a storage section that stores reference data for changing focus positions according to the contrast of image. The camera body includes an imaging device to output a video signal representing subject's image and a second computing section for measuring the contrast of the image based on its own predetermined evaluated AF frequency during the focusing operation and calculating a correction value based on the shooting parameter and the reference data associated with the highest contrast, thereby changing the focus positions according to the correction value calculated.