To improve a working circumstance and to improve mounting workability to a car body panel by preventing production of cellulose dust and layer peeling on a cutting work part in trim cutting work and pierce-cutting work of an acoustic material.

Dust and layer peeling are prevented by applying a cutting process by a trim-cutting blade 50 in a state of improving a binding property between cellulose by moistening the acoustic material M with water before trim-cutting work along a trim-cutting line A of the acoustic material M. Additionally, it is possible to shorten drying time by carrying out the cutting process while evaporating moisture of the trim-cutting work part by using the trim- cutting blade 50 and a hot blade.