The drag reduction performance of a half airfoil attached to a trailer and the roof fairing at different positions was experimentally investigated in a wind tunnel. Half airfoils have NACA 0009 and NACA 0012 cross-section and the roof fairing position is changed from -4.5 mm to +4.5 mm. Smoke wire and surface oil flow visualization were also performed to elucidate the flow characteristic around the truck-trailer with drag reduction devices. While the drag reduction rate of the truck trailer with half airfoil is up to 10% higher than that of alone truck-trailer at all Reynolds number ranges, drag reduction of the truck trailer with the half airfoil and the roof fairing was exceeded 30% as compared to the alone truck trailer. Drag coefficient results indicated that the half NACA 0009 and NACA 0012 airfoil has an almost similar trend at the zero-roof fairing position. Laminar separation bubble formation was observed on the surface of roof fairing with the help of surface oil flow visualization.