To securely position and fix a can body to a mandrel, and smoothly perform attaching/detaching work of the can body to/from the mandrel in a trimmer.

A trimmer 21 is provided with a rotatable cylindrical mandrel 22 around which a can body is inserted t6 be positioned, and a rotatable adjacent shaft 5 having an axial line parallel to the mandrel 22, so the mandrel 22 and the adjacent shaft 5 are rotated to each other to engage a circular mandrel side blade part 8 provided on a base end part of the mandrel 22 with an arc-shaped shaft side blade part 12 provided on an outer circumferential part of the adjacent shaft 5, having an opening edge of the can body between them, for cutting off the opening edge, and forming it. In this case, the mandrel 22 has an opening end at a tip part, and a suction hole 23g to suck the can body at the opening end, and plural recessed parts are formed on an outer circumferential surface.