A display system includes a host apparatus having a video interface circuit and a display apparatus operated by feed of a video image and power from the host apparatus, and also has a communication function for receiving and transmitting data between the host apparatus and the display apparatus. The rear-wheel steering angle control device includes a target rear-wheel steering angle calculating device which has a variable coefficient inputting device. Two strike lines are provided on an artificial turf for accommodating both right and left-handed users. A water purification system incorporating said filter said water purification system capable of removing about 99% of all particles not less than 1. The concave portion has a surface including an evanescent light generating portion.