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.