Provided is a mouthpiece for an extruder provided at an extruder extruding a flowable molding material, including: a molding material flow passage; a molding material extrusion port formed at a front end of the molding material flow passage; and one or plural flow resistance members provided to advance into and withdraw from the molding material flow passage, the advancing and the withdrawing being performed by an operation at the outside of the mouthpiece for the extruder.