A refrigerating and air-conditioning system includes a plurality of independent refrigerating and air-conditioning apparatuses each including a refrigerant circuit and a defrosting unit, and further includes a system controller managing the apparatuses in an integrative manner. The system controller includes a defrosting operation control unit. When a time interval between an estimated defrosting start time calculated for a given refrigerating and air-conditioning apparatus and a subsequent estimated defrosting start time calculated for another refrigerating and air-conditioning apparatus is less than or equal to a predetermined target start time interval, the defrosting operation control unit transmits a defrosting start instruction signal to the defrosting unit of the given refrigerating and air-conditioning apparatus.