Functional near-infrared spectroscopy (fNIRS) is an optical neuroimaging method for recording cerebral hemodynamics. Tolerance of motion is considered an advantage of fNIRS when compared with other imaging techniques. However, fNIRS signals are often contaminated by scalp blood flow (SBF) signals due to motion of the subject. In the present study, we recorded changes in the concentrations of oxygenated and deoxygenated hemoglobin by multidistance source-detector probes during whole body tilting with the head and trunk fixed, and demonstrated that the change in body direction against gravity causes SBF signal contamination. Non-negligible parallel changes in oxygenated and deoxygenated hemoglobin during trunk tilt were observed in long-distance channels (conventional 30 mm), as well as those in short-distance channels (15 mm) reflecting SBF changes. Because the tilt angle-dependent changes in the long channels were correlated highly with those in the short channels, the fluctuation caused by the trunk tilt could be considered SBF signal contamination. The contamination was successfully removed by a multidistance method and by a hemodynamic modality separation method.