A camera system including an electronic flash device with a slave emission function, includes an electronic flash device including: a light-receiving unit for receiving a steep optical signal; a light-emitting unit for slave-emitting illumination light toward an object in response to the optical signal received by the light-receiving unit; a timer for starting a time measurement operation in response to the optical signal input to the light-receiving unit, and permitting an operation of the light-emitting unit after an elapse of a predetermined period of time; an attachment member used for attaching/detaching the device to/from a camera body; and a data communication function unit for exchanging various data including photographing information with the camera body via the attachment member; and a camera body electrically connected to the electronic flash device. In the camera system, the data communication function unit delays a synchronous time set by the camera body side in correspondence with the measurement time of the timer.