SELECTIVE CATALYTIC REDUCTION SYSTEM

An SCR system that can detect a NO x concentration accurately irrespective of an operation state of an engine is provided. The SCR system including: an SCR device 103 provided in an exhaust pipe 102 for an engine E; a dosing valve 104 that injects urea solution on an upstream side of the SCR device 103; a NO x sensor 110 provided in the exhaust pipe 102; and an urea solution injection control unit 127 that controls a urea solution injection quantity according to a NO x concentration value detected by the NO x sensor 110 includes a pressure estimation unit 131 that estimates a NO x sensor pressure that is a pressure inside the exhaust pipe 102 at a position where the NO x sensor 110 is provided, and a NO x concentration detection value correction unit 136 that corrects the NO x concentration value detected by the NO x sensor 110, according to the NO x sensor pressure estimated by the pressure estimation unit 131.