To replace a unit blade and a fixing means for fixing the blade simultaneously.

Unit blades 12 are fitted to a drum main body 18 individually freely replaceably. Blade change structure makes it also possible to replace an unit blade fixing body 19 which is a fixing means for fixing the blade 12. The blade 12 is fitted between the drum main body 18 and the blade fixing body 19, which is fixed to the drum main body by an attaching/detaching body. So long as the blade fixing body 19 is not fixed to the drum main body 18, the blade 12 can not be fixed to the drum main body 18. To the contrary, so long as the blade fixing body 19 is not separated from the drum main body 18, the blade 12 can not be separated from the drum main body 18. The blade fixing bodies 19 and the blades 12 form a cylindrical body which forms the periphery of the drum.