A belt drive system for a mechanical cleaning device that require counter-rotating brushes andor scrubbers, comprising two belts 42 and 44, a drive shaft 36, a pulley 32, and two rotary brushes 22 and 24. The display control unit decides a display language based on the identification information read out by the interface and changes a display language on the authenticating display screen according to the decided language. A transfer command having a highest priority level is selected.