The purpose of this study was to investigate the relationship between the mandibular positions and the habitual mandibular opening and closing movements in normal subject using the newly developed electric mandibular movement analyzing device(Saphon Visi-Trainer C-II.Tokyo Shizaisha Inc. Tokyo, Japan) One of the cause of the temporomandibular joint dysfunction has been considered abnormal mandibular positions especially the abnormal deviation between intercuspal position from retruded contact position. The subjects in this study were consisted of 55 young adults in 20 decade who had normal occlusion, no prosthodontic restorations and no history of disturbance or pain on temporomandibular joint and masticatory muscles. The results were as follows : 1. The deviations of intercuspal position from retruded contact position were 0.23mm in frontal view and 1.02mm in sagirral view. 2. The larger the deviation of intercuspal position from the retruded contact position, the higher the proportion of uncoincidence of the habitual nandibular closing and opening trajectories was, and the proportion was higher in sagittal view than frontal view, 10mm opening than 5mm opening. 3. Correlation between the deviation of intercuspal position from retruded contact position and uncoincidence rate of the habitual mandibular closing and opening trajectories was higher in frontal view than sagittal view.