This invention provides a technique of stably focusing on a major object without any sense of discomfort regardless of differences in lens unit type in a camera body on which a lens unit can be detachably mounted. For this purpose, the type of lens unit connected to the camera is determined. Cutoff frequencies are then set for a low-pass filter and high-pass filter on the basis of the determination result. With regard to frequency component data in predetermined area of an image sensor, a peak hold circuit, integrator, and difference peak hold circuit each generate evaluate value information. A camera microcomputer transmits the obtained evaluate value information to a lens microcomputer in the lens unit.