A cleaning method for removing unnecessary matter accumulated on a surface on the bottom of a recess so as to clean the surface. An adhesive surface on a projection projected from an elongated base member is brought into contact with the unnecessary matter on the surface to be cleaned and is separated forcibly from the surface to be cleaned by application of tension to the elongated base member, whereby the unnecessary matter is lifted off the recessed surface to be cleaned. Disclosed also is a cleaning cassette for cleaning the bottom surface of a recess by removing unnecessary matter from the surface, having an elongated tape-like base member carrying a plurality of projections each having an adhesive end surface which is adapted to be pressed onto the unnecessary matter accumulated on the surface to be cleaned.