Safety and comfort are importance concepts for designers of vehicle seats and instrument panels. There have been a lot of researches on comfortable sitting postures, however, relatively a few researchers have tried to find a desirable driving posture in consideration of both comfort and safety. This study investigates a relationship between comfort and safety of sitting posture of a driver. Since a seat is closely related to comfort, the angular data of comfortable sitting posture were obtained through the correlation between the seat and the driver. In order to acquire the data of safe sitting posture, computer simulations were performed for various seatback angles. Based on comparing and analyzing the data obtained, the optimal sitting posture is suggested for both comfort and safety aspects.