A refrigerating and air-conditioning apparatus performs, even during a heating operation under air conditions leading to formation of frost, a defrosting operation while simultaneously continuing a heating operation and that improves comfort through heating by ensuring an appropriate amount of ventilation. A plurality of refrigeration cycles that are capable of independently performing a heating operation and a defrosting operation, are provided. A ventilation damper of an indoor unit in which a refrigeration cycle that performs a defrosting operation is installed is closed during a defrosting operation, and a ventilation damper of an indoor unit in which a refrigeration cycle that performs a heating operation is installed is controlled to achieve a required amount of ventilation corresponding to the indoor ventilation state.