Diesel engine with high fuel efficient potential raises the expectations for reducing the carbon dioxide emission and improving an air environment. The emission gas purification absolutely requires after treatment systems such as DPF (Diesel Particulate Filter), and platinum catalysts, used for the systems, enjoy an increasing demand. From view points of both resource restriction and economical efficiency, diminishing the quantity consumed of platinum is an urgent task. Various approaches have been conducted on systems, such as microstructure control of filter, catalysts and supports.