The present invention provides a transport refrigeration unit which can prevent a decrease in an inside temperature during defrosting, can perform defrosting within a short time, and can ensure reliability by appropriately adjusting a condensing capacity during a cooling operation, and suppressing frequent starting and stopping of a compressor during thermo-on/off. In a transport refrigeration unit 1 having a heat pump-type warming function, two of a plurality of heat exchangers 8A to 8C are disposed in parallel with each other outside a refrigerator as outside heat exchangers 8A and 8B, one of the plurality of heat exchangers is disposed inside the refrigerator as an inside heat exchanger 8C, and when the outside heat exchangers 8A and 8B are frosted during a heat pump warming operation in which the outside heat exchangers 8A and 8B are caused to function as evaporators, and the inside heat exchanger 8C is caused to function as a condenser, a defrosting operation is performed by stopping refrigerant distribution to the inside heat exchanger 8C, and causing one of the outside heat exchangers 8A and 8B to function as a condenser, and another one to function as an evaporator.