A steering system for a construction vehicle, said steering system being provided with steering hydraulic cylinders as actuators arranged for performing steering of said vehicle, a pilot-operated directional control valve arranged for controlling a direction and amount of pressure oil to be fed to said steering hydraulic cylinders, and a steering-wheel-operated signal generation means provided with a rotationally-operable steering wheel arranged such that by rotational operation of said steering wheel, a pilot signal is generated effective to switch an operated position and opening area of said pilot-operated directional control valve, wherein said steering system comprises a lever-operated signal generation means provided with a tilt-operable steering lever adapted to generate by tilt operation of said lever a pilot signal for switching the operated position and opening area of said pilot-operated directional control valve, selector valves (13a, 13b) switchable such that the pilot signal from the steering-wheel-operated signal generation means or the pilot signal from the lever-operated signal generation means can be selectively outputted to said pilot-operated directional control valve, a lever-operated manual switching means arranged for switching said selector valves (13a, 13b) such that by manual operation, the pilot signal from said lever-operated signal generation means can be outputted to said pilot-operated directional control valve to permit steering said vehicle by tilt operation of said steering lever, and an automated switching means (16, i) arranged for preferential control by said steering wheel to automatically switch said selector valves (13a, 13b) such that upon rotational operation of said steering wheel, the pilot signal from said steering-wheel-operated signal generation means can be outputted to the pilot-operated directional control valve even when said selector valves (13a, 13b) have been switched by the manual operation of said manual switching means to permit outputting the pilot signal from said lever-operated signal generation means to said pilot-operated directional control valve, wherein said selector valves (13a, 13b) are each constructed with a combination of mutually-opposing signal receiving ports such that by guiding pilot oil to one of said signal-receiving ports of each selector valve (13a, 13b), the pilot signal from said lever-operated signal generationmeans can be outputted to said pi lot-operated directional control valve and by guiding pilot oil to the other signal-receiving port of said mutually opposing signal receiving ports of each selector valve (13a, 13b), said selector valves (13a, 13b) can be switched to permit outputting the pilot signal from said steering-wheel-operated signal generation means to said pilot-operated directional control valve even when pilot oil has been guided to said one signal-receiving port of each selector valve (13a, 13b); said lever-operated manual switching means comprises a lever-operated manual switch arranged for permitting steering said vehicle by tilt operation of said steering lever and a selector-valve-switching valve switchable by a control signal from the lever-operated manual switching means to permit guiding pilot oil to the one signal-receiving port of each selector valve (13a, 13b) such that the pilot signal from said lever-operated signal generation means can be outputted to said pilot-operated directional control valve; and said automated switching means (16, i) arranged for preferential control by the steering wheel comprises a cancel valve arranged in a flow passage (j), which feeds pilot oil from a pilot pump to said selector-valve-switching valve, arranged such that, when a pilot signal from said steering-wheel-operated signal generation means adapted to switch said pilot-operated directional control valve is outputted to a signal-receiving port of said cancel valve and said cancel valve is switched, said selector valves (13a, 13b) are switched to guide pilot oil from said pilot pump to the other signal-receiving port of each selector valve (13a, 13b) and effective to permit outputting the pilot signal from said steering-wheel-operated signal generation means to said pilot-operated directional control valve.