A slew working vehicle (1) is equipped with a left traveling motor (13) and a right traveling motor (14) both for driving left and right traveling devices (2L, 2R) and controls the traveling motors (13, 14) independently with left and right hydraulic directional control valve (15, 16). A throttle valve(55)is provided in a pilot oil passage (54) to allow the oil path to pass in series through the hydraulic directional control valves (15, 16) downstream of the throttle valve (55) and to connect with a drain oil passage (30). This vehicle is also provided with a travel-alarming pressure switch (61) which operates by the pilot oil preessure which is the oil pressure in the pilot oil passage (54) between the throttle valve (55) and the upstream one of the left and right hydraulic control valves (15, 16).