This paper describes a rendering method that simultaneously renders both volumetric and polygonal objects. It is also possible to render volumetric objects intersected by polygonal ones or volumetric ones in the same scheme. In the proposed method, a scene including volumes and polygons overlapping each other is rendered using a ray-volume buffer that stores the colors and transmittance of a ray at each voxel. Polygons inserted in a volume are rendered by mapping the ray-volume data as 3D texture. We rendered a mixed scene of two volumes in the same scheme by considering a volume overlapping with another volume as multiple layers of translucent polygons. The ray-volume buffer method treats volumetric objects as polygons with textures. Therefore, the method can be realized using conventional graphics pipeline techniques by generating a ray volume for a 3D texture. Another feature of this method is that ray volumes can be generated without consideration of the intersection with polygons or volumes.