A transport refrigeration system, the transport refrigeration system comprising: a generator ; a power generation engine that drives the generator ; a refrigerator that adjusts a temperature of a storage space , an electric power converter that converts an electric power generated by the generator into a drive output for the refrigerator and supplies the drive output to the refrigerator ; an output control unit that controls the drive output from the electric power converter to the refrigerator to adjust an operation state of the refrigerator ; a characteristic estimation unit that estimates a refrigerator characteristic of the refrigerator according to an outside air temperature and a temperature of the storage space ; and an output calculation unit that calculates the drive output as a target drive output that optimizes an energy efficiency of the entire system based on the refrigerator characteristic estimated by the characteristic estimation unit , a preset engine characteristic of the power generation engine , and a preset generator characteristic of the generator , wherein the output control unit controls the drive output to approach the target drive output calculated by the output calculation unit , characterized in that , when the target drive output calculated by the output calculation unit is lower than a required drive output of the refrigerator required for temperature adjustment of the storage space , the required drive output being either a fixed value or a value variable in accordance with the temperature difference between the outside air temperature and the temperature of the storage space , the required drive output is set to the target drive output and then the output control unit is configured to control the drive output to approach the required drive output. a generator ; a power generation engine that drives the generator ; a refrigerator that adjusts a temperature of a storage space , an electric power converter that converts an electric power generated by the generator into a drive output for the refrigerator and supplies the drive output to the refrigerator ; an output control unit that controls the drive output from the electric power converter to the refrigerator to adjust an operation state of the refrigerator ; a characteristic estimation unit that estimates a refrigerator characteristic of the refrigerator according to an outside air temperature and a temperature of the storage space ; and an output calculation unit that calculates the drive output as a target drive output that optimizes an energy efficiency of the entire system based on the refrigerator characteristic estimated by the characteristic estimation unit , a preset engine characteristic of the power generation engine , and a preset generator characteristic of the generator , wherein the output control unit controls the drive output to approach the target drive output calculated by the output calculation unit , characterized in that , when the target drive output calculated by the output calculation unit is lower than a required drive output of the refrigerator required for temperature adjustment of the storage space , the required drive output being either a fixed value or a value variable in accordance with the temperature difference between the outside air temperature and the temperature of the storage space , the required drive output is set to the target drive output and then the output control unit is configured to control the drive output to approach the required drive output. <EOS>