Ray tracing is a global illumination based rendering method widely used in computer graphics. Although it generates photo-realistic images, it requires a large number of computations. In ray tracing, the ray-object intersection test is one of the dominant factors for the processing speed. To accelerate the intersection test, we propose a new method based on a plane-sphere intersection algorithm, and show a hardware system using an FPGA. The computations used in the method are highly pipelined and parallelized by optimizing the balance between the computation speed and the memory data bandwidth. As a result, the prototype makes full use of 512 DSP cores built in Xilinx Vertex-4 SX FPGA, and the average utilization of the DSP cores is close to 90%. The simulation results show that the proposed system running at 160MHz performs the intersection test a few hundred times faster than a commodity PC with a 3.4GHz Pentium 4.