An image-taking apparatus on which lens apparatuses are detachably attachable, the image-taking apparatus comprising: an image pickup element which photoelectrically converts an object image; an image-taking section which carries out image-taking by controlling the image pickup element in a calibration mode for calibrating a parameter relating to image-taking and a normal image-taking mode for carrying out an image-taking operation using said parameter, wherein, in the calibration mode, a lens apparatus of the lens apparatuses is attached to the image-taking apparatus, and wherein, in the normal image-taking mode, the lens apparatus is attached to the image-taking apparatus; a first control section which, in said calibration mode, makes the image-taking section take a plurality of images of an object with said parameter different from each other, said parameter being successively shifted by a predetermined amount so as to include a preset reference value of said parameter; a memory; a second control section which, in said calibration mode, stores information on said parameter corresponding to an image selected by a user among the plurality of images in said memory, and stores, in said calibration mode, said information on said parameter as being associated with identification information in the memory; and a third control section which, in said normal image-taking mode, determines whether said information on said parameter is stored in the memory as being associated with the identification information, and determines that a corrected result of focus detection is to be used for the image-taking in said normal image-taking mode if said information on said parameter is stored as being associated with the identification information, wherein the corrected result of focus detection is obtained from a result of focus detection at the time of image taking in the normal image-taking mode corrected on the basis of said information on said parameter stored in the memory; wherein said information on said parameter is an amount of shift in said parameter from said reference value, said identification information is received from the lens apparatus by communications, the parameter is an amount of defocus of an image-taking optical system which forms the object image, and the reference value is an amount of defocus corresponding to an in-focus state in focusing control of the image-taking optical system in the image taking controlled by the first control section. an image pickup element which photoelectrically converts an object image; an image-taking section which carries out image-taking by controlling the image pickup element in a calibration mode for calibrating a parameter relating to image-taking and a normal image-taking mode for carrying out an image-taking operation using said parameter, wherein, in the calibration mode, a lens apparatus of the lens apparatuses is attached to the image-taking apparatus, and wherein, in the normal image-taking mode, the lens apparatus is attached to the image-taking apparatus; a first control section which, in said calibration mode, makes the image-taking section take a plurality of images of an object with said parameter different from each other, said parameter being successively shifted by a predetermined amount so as to include a preset reference value of said parameter; a memory; a second control section which, in said calibration mode, stores information on said parameter corresponding to an image selected by a user among the plurality of images in said memory, and stores, in said calibration mode, said information on said parameter as being associated with identification information in the memory; and a third control section which, in said normal image-taking mode, determines whether said information on said parameter is stored in the memory as being associated with the identification information, and determines that a corrected result of focus detection is to be used for the image-taking in said normal image-taking mode if said information on said parameter is stored as being associated with the identification information, wherein the corrected result of focus detection is obtained from a result of focus detection at the time of image taking in the normal image-taking mode corrected on the basis of said information on said parameter stored in the memory;