A construction machine comprising: an engine; a variable displacement hydraulic pump driven by the engine; a hydraulic actuator; a selector valve capable of establishing and interrupting of communication of a line (15, 16) connecting the hydraulic pump with the hydraulic actuator; an unloading valve that is provided in a line branched from a delivery line of the hydraulic pump and connecting to a tank and that is opened according to a pilot pressure acting on a pilot pressure receiving section; a pilot pump driven by the engine; a pilot control valve that is provided in a pilot line connecting a delivery port of the pilot pump with the pilot pressure receiving section and that controls the pilot pressure acting on the pilot pressure receiving section; a controller that controls opening of the pilot control valve; and a key switch capable of being switched between a key OFF state, a key ON state for giving an instruction about starting of the controller, and an engine ON state for giving an instruction about starting of the engine, the controller opening the pilot control valve in case the key switch is operated from the key OFF state to the key ON state, characterized in that the construction machine includes an electric pump having a delivery port connected to a line part of the pilot line, the line part connecting the delivery port of the pilot pump with the pilot control valve, a motor that drives the electric pump, and a temperature sensor for measuring a temperature of a hydraulic working fluid delivered from the pilot pump, and the controller is configured to start driving of the motor in case the key switch is operated from the key OFF state to the key ON state and the temperature of the hydraulic working fluid measured by the temperature sensor is lower than a predetermined temperature. an engine; a variable displacement hydraulic pump driven by the engine; a hydraulic actuator; a selector valve capable of establishing and interrupting of communication of a line (15, 16) connecting the hydraulic pump with the hydraulic actuator; an unloading valve that is provided in a line branched from a delivery line of the hydraulic pump and connecting to a tank and that is opened according to a pilot pressure acting on a pilot pressure receiving section; a pilot pump driven by the engine; a pilot control valve that is provided in a pilot line connecting a delivery port of the pilot pump with the pilot pressure receiving section and that controls the pilot pressure acting on the pilot pressure receiving section; a controller that controls opening of the pilot control valve; and a key switch capable of being switched between a key OFF state, a key ON state for giving an instruction about starting of the controller, and an engine ON state for giving an instruction about starting of the engine, the controller opening the pilot control valve in case the key switch is operated from the key OFF state to the key ON state, characterized in that the construction machine includes an electric pump having a delivery port connected to a line part of the pilot line, the line part connecting the delivery port of the pilot pump with the pilot control valve, a motor that drives the electric pump, and a temperature sensor for measuring a temperature of a hydraulic working fluid delivered from the pilot pump, and the controller is configured to start driving of the motor in case the key switch is operated from the key OFF state to the key ON state and the temperature of the hydraulic working fluid measured by the temperature sensor is lower than a predetermined temperature.