A steering system includes a rack shaft, a housing, an electric motor, a control device, and a speed reduction mechanism that applies a moving force in the axial direction to the rack shaft with the speed of rotation of the electric motor reduced. The housing has a rack shaft housing portion and a speed reduction mechanism housing portion. The electric motor has: a motor case fixed to the housing; a plurality of stator cores disposed annularly in the motor case; coil windings wound around the plurality of stator cores; and a rotor. The motor case is formed with a water introduction hole that introduces water that has entered the speed reduction mechanism housing portion into the motor case. The control device has a detector that detects entry of water into the motor case.