The southwestern part of the Ryukyu arc-trench system to the west of 126 degree E is obviously bent northwards horizontally. The mechanism of this horizontal bending has been discussed in the literature, but it is still ambiguous. The West Philippine Basin (WPB) is generally believed to be produced by spreading along the Central Basin Ridge (CBR). However, the CBR does not extend to the northwestern corner of the WBP. Previous geomagnetic and geomorphological studies suggested that the CBR terminates or is displaced at its northwestern end. However, the detailed picture is still unclear. In this paper, we have examined bathymetry, gravity and seismicity in and around the northwestern corner of the WPB, and discovered a NE-trending right-handed strike-slip fault system which can be used to interpret the horizontal bending of the southwestern part of the Ryukyu arc-trench system. A plausible model showing how the right-handed fault system results in the bending of the Ryukyu arc-trench system is demonstrated. As the southeastern part of the right-handed strike-slip fault system, the Luzon-Okinawa Fault Zone, which is an obvious fault zone between the Luzon and Okinawa islands, is described in terms of bathymetric contours and profiles along some cruise lines. The Luzon-Okinawa Fault Zone is the main cause of the termination of the CBR.