Data related to an object distance which is sent from a camera apparatus is captured. A focus lens position instructed value CL is calculated based on an object distance instructed value CD and a zoom position information value ZP. An object distance returned value PL to be transmitted to the camera apparatus is obtained based on a current lens position CF and the zoom position information value ZP. Whether the focus lens position instructed value CL is equal to the lens position CF or not is determined. When the focus lens position instructed value is not equal to the lens position, a focus lens is moved in accordance with the focus lens position instructed value CL is performed. When the focus lens position instructed value is equal to the lens position, lens driving processing is not performed.