The accessory apparatus includes an accessory communicator providing a notification channel, a first data communication channel and a second data communication channel. The accessory controller transmits, in response to receiving a transmission request from an image-capturing apparatus through the notification channel, accessory data to the image-capturing apparatus through the first data communication channel and receives camera data transmitted from the image-capturing apparatus through the second data communication channel. The accessory controller has a function of detecting a camera communication error in the camera data and is configured to, when detecting the camera communication error, transmit accessory error information to the image-capturing apparatus and erase the accessory data stored in an accessory data buffer.