A selective catalytic reduction system includes a selective catalytic reduction device on an exhaust pipe of an engine, a urea solution tank that stores a urea solution, a float-type urea solution level sensor in the urea solution tank, a dosing valve on the exhaust pipe upstream of the selective catalytic reduction device, a urea solution injection control section that controls an amount of urea solution to be injected through the dosing valve in accordance with an amount of NOx discharged from the engine, an inclination sensor that detects an inclination angle of the urea solution tank relative to horizontal, and an inclination angle correcting section that corrects a liquid level of the urea solution, the liquid level being detected by a detection unit from the position of a float, with the inclination angle detected by the inclination sensor.