Abstract: A reel changer of a web-fed printing press includes a load-bearing axle and a carrying arm having at least two carrying-arm segments. A printing-material reel may be mounted or clamped between the carrying-arm segments of the carrying arm. The printing-material reel is displaceable relative to the load-bearing axle using the carrying-arm segments in a production mode. A control system and a safety system which operates independently of the control system both monitor the relative spacing between the carrying-arm segments and blocks the respective carrying-arm segments in the event of an impermissible spacing deviation in the production mode. The safety system includes a separate distance measuring device dedicated to each carrying-arm segment, which distance measuring devices interact with an evaluation device.