An accessory and an electronic device enabling retransmission of data from the electronic device to the accessory when a checksum error occurs in the accessory. An accessory controller of the accessory determines whether or not a checksum received from the camera and a first checksum calculated from data received from the camera match. In a case where the checksums match, the accessory controller calculates a second checksum, whereas in a case where the checksums do not match, the accessory controller calculates a third checksum. The accessory controller transmits the second checksum or the third checksum to the camera according to a result of the determination.