A wide field of vision is important for driver safety and vehicle operability. However, the window area of vehicles is limited. Therefore, we developed head-tracked retro-reflective projection technology that displays vehicle blind spot information. The system enables the driver to observe the surroundings in the blind spot as if seeing through the inner wall of the vehicle. The system uses a head-mounted projector and multiple cameras. We describe the system design, the implementation of a prototype, and performance evaluation experiments. Early experiments showed that the system effectively displayed the blind spot information corresponding to the operator's looking around motion.