A camera body includes an imaging unit for generating image data from an optical signal incident via the interchangeable lens, a detector for detecting a light quantity of the optical signal, a controller for setting an aperture value of a diaphragm of the interchangeable lens and an exposure condition which is a setting relating to exposure other than a setting of the diaphragm, a sending unit for sending a control signal for control with the set aperture value to the interchangeable lens, and a mode setting unit for selecting one from a plurality of operating modes. The plurality of operating modes includes a first mode for automatically adjusting the aperture value of the diaphragm and the exposure condition according to the detected light quantity during capturing of a moving image, and a second mode for automatically adjusting the aperture value with the exposure condition being fixed according to the detected light quantity during capturing of the moving image. An average drive speed of the diaphragm for automatically adjusting the aperture value in the second mode is slower than that in the first mode.