A steering system for steering front and rear wheels of an industrial vehicle has an upper frame rotatably coupled on an upper side of a lower frame, a steering system rotating the front and rear wheels in a predetermined direction as a steering wheel is rotated, a differential driving unit mounted to each of the wheels and differentially driving the left wheel and the right wheel according to a load applied to the wheels, a boom assembly having a boom length adjuster, and an upper frame pivoting unit provided between the lower and upper frames and rotating the upper frame in relation to the lower frame.