The image-capturing apparatus includes a camera communicator to providing, with the accessory apparatus, three channels that are a notification channel, a first data communication channel used for transmitting accessory data from the accessory apparatus to the image-capturing apparatus, and a second data communication channel used for transmitting camera data from the image-capturing apparatus to the accessory apparatus. A camera controller is configured to, in response to detecting a start bit included in each of frames of the accessory data and indicating a start of each frame, transmit one frame of the camera data to the accessory apparatus through the second data communication channel and perform detection of the start bit regardless of whether or not during transmitting the camera data to the accessory apparatus.