To provide a cleaning method, in cleaning of a glass tube composite body having an alkaline resistant resin part, particularly when executing the cleaning of using an alkaline detergent.

The glass tube composite body (100) having the alkaline resistant resin part (11) is cleaned by using the alkaline detergent. Thus, since the glass tube composite body (100) is cleaned by using the alkaline detergent, the glass surface-etching effect can be provided, so that the glass surface-stain removing effect can be improved.