This paper described about the measuring error on working depth of the Real-time soil sensor (RTSS). It is necessary for accurately evaluating to observe the variation on the working depth, because the RTSS run in various real field conditions, such as soft or hard and even or uneven, and the RTSS has various using objective. In this paper, the RTSS run on asphalt with steps while the three-point hitch was free and position-controlled. In position-controlled, the measuring depth that is the length between the surface on the track running and the measuring surface was greater influenced from tractor orientation than in free. The result will be inapplicable on a real field, and hence, an experiment on a field will be planned.