Exhaust gas purifying device of work machine

An exhaust gas purifying device of a work machine, including a reduction catalyst that is placed in an exhaust flow passage of an exhaust gas of an engine and uses a reducing agent to reduce and purify nitrogen oxides in the exhaust gas, and a reducing agent injector to inject the reducing agent into the exhaust flow passage, the exhaust gas purifying device of the work machine comprising:

• a urea water tank that stores the reducing agent;
• a concentration sensor that has a sensing part placed within the urea water tank to detect a concentration of the reducing agent;
• an injection valve that injects the reducing agent toward the sensing part;
• a reducing agent pump that supplies the reducing agent in the urea water tank to the injection valve;
• a pressure sensor that detects a discharge pressure of the reducing agent pump;
• and
• an air-bubble removal controller that controls, based on a value detected by the concentration sensor and a value detected by the pressure sensor, injection of the reducing agent performed by the injection valve.