Recently, there are great requirements for ultra fine powder in fields that use advanced materials, for example, electric parts in Information Technology (IT) industry. Especially, the request for the diameter control of ultra fine powder is increasing. Pneumatic type ultra fine powder separator, classifier, is one of the equipment which meet this request. But there is no clarified study on the flow condition that realizes high performance. In this study, a new pneumatic type ultra fine classifier is proposed and the relation between the performance and the flow condition is investigated by flow visualization with the tuft grid and oil dot methods and the measurement of gas velocity. Based on the results, it was known that the new classifier has a large swirling flow velocity which is able to classify ultra fine particles accurately.