A hybrid construction machine comprising: an engine; a generator motor that is driven by the engine; a hydraulic pump of a variable capacity type that is driven by the engine; a power storage unit that is charged by power generation operation of the generator motor; a power storage temperature detecting unit that detects power storage temperature, which is a temperature of the power storage unit; a power storage SOC detecting unit that detects a power storage SOC, which is a charging state of the power storage unit; a pump-pressure detecting unit that detects a pump pressure for horsepower control of the hydraulic pump; a hydraulic load unit (10, 11) that applies a hydraulic load to the hydraulic pump; characterized by a control unit that performs warming-up control for raising temperatures of the power storage unit and the hydraulic oil, wherein the control unit includes: a first warming-up control unit (3, 15) that calculates warming-up time charging power, which is charging power during warming up from the power storage SOC and the power storage temperature, and causes the generator motor to perform the power generation operation, thereby charging the power storage unit on the basis of the calculated warming-up time charging power; and a second warming-up control unit that applies, during the power generation operation, the hydraulic load to the hydraulic pump by the hydraulic load unit (10, 11) and performs the horsepower control of the hydraulic pump using a value obtained by subtracting the warming-up time charging power from preset warming-up time pump horsepower. an engine; a generator motor that is driven by the engine; a hydraulic pump of a variable capacity type that is driven by the engine; a power storage unit that is charged by power generation operation of the generator motor; a power storage temperature detecting unit that detects power storage temperature, which is a temperature of the power storage unit; a power storage SOC detecting unit that detects a power storage SOC, which is a charging state of the power storage unit; a pump-pressure detecting unit that detects a pump pressure for horsepower control of the hydraulic pump; a hydraulic load unit (10, 11) that applies a hydraulic load to the hydraulic pump; characterized by a control unit that performs warming-up control for raising temperatures of the power storage unit and the hydraulic oil, wherein the control unit includes: a first warming-up control unit (3, 15) that calculates warming-up time charging power, which is charging power during warming up from the power storage SOC and the power storage temperature, and causes the generator motor to perform the power generation operation, thereby charging the power storage unit on the basis of the calculated warming-up time charging power; and a second warming-up control unit that applies, during the power generation operation, the hydraulic load to the hydraulic pump by the hydraulic load unit (10, 11) and performs the horsepower control of the hydraulic pump using a value obtained by subtracting the warming-up time charging power from preset warming-up time pump horsepower. a first warming-up control unit (3, 15) that calculates warming-up time charging power, which is charging power during warming up from the power storage SOC and the power storage temperature, and causes the generator motor to perform the power generation operation, thereby charging the power storage unit on the basis of the calculated warming-up time charging power; and a second warming-up control unit that applies, during the power generation operation, the hydraulic load to the hydraulic pump by the hydraulic load unit (10, 11) and performs the horsepower control of the hydraulic pump using a value obtained by subtracting the warming-up time charging power from preset warming-up time pump horsepower.