A camera system includes an interchangeable lens and a camera body. The camera body includes an imaging unit, a contrast detection unit, a defocusing amount detection unit, and a body microcomputer. The contrast detection unit is configured to detect a contrast value from an image signal of a subject acquired by the imaging unit, and is configured to detect the focal state of an optical image on the basis of the contrast value. The defocusing amount detection unit is configured to detect the focal state of the optical image by phase difference detection method. The body microcomputer is configured to select either the contrast detection unit or the defocusing amount detection unit on the basis of lens information on the interchangeable lens side.