Provided are a camera system, a camera, a lens, an accessory, and an accessory detection method of a camera system capable of simply and quickly detect presence or absence of an attachment of the accessory and a type of the accessory. Data for accessory detection is transmitted from the lens to the camera. In a case where the accessory is attached between the lens and the camera, the accessory relays the data for accessory detection. At the time of relaying the data for accessory detection, the accessory adds own accessory information to update the data for accessory detection. The camera detects the presence or absence of the attachment of the accessory and the number of attachments of the accessory based on the received data for accessory detection. Further, in a case where the attachment is detected, the camera acquires information on the attached accessory.