Hydraulic system of construction machine

A hydraulic system of a construction machine, comprising:

• a variable displacement main pump;
• control valves interposed between the main pump and hydraulic actuators, each control valve including pilot ports;
• first solenoid proportional valves connected to the pilot ports of the control valves;
• operation devices to move the control valves, each operation device outputting an electrical signal corresponding to an operating amount of the operation device;
• a controller that controls the first solenoid proportional valves based on the electrical signals outputted from the operation devices;
• a regulator that changes a displacement of the main pump based on a signal pressure;
• a second solenoid proportional valve connected to an auxiliary pump by a primary pressure line, the second solenoid proportional valve outputting a secondary pressure as the signal pressure to the regulator through a secondary pressure line;
• and
• a switching valve interposed between the auxiliary pump and the first solenoid proportional valves, the switching valve including a pilot port that is connected to the secondary pressure line by a pilot line, the switching valve switching between a closed position and an open position in accordance with a pilot pressure led to the pilot port.