A die has two surfaces, in a forming material supplying surface which is one surface, a plurality of back holes to introduce a forming material of a honeycomb formed body into the die are formed, and in a honeycomb formed body extruding surface which is the other surface, lattice-shaped slits corresponding to cell partition walls are formed, the back holes communicate with the slits in slit intersecting portions of the slits, polygonal cell blocks defined by the slits include chamfered portions in which parts of corner portions and the like are chamfered at a chamfering angle θ of 1.0 to 8.0° to the extruding direction, from the honeycomb formed body extruding surface toward a slit depth direction, and straight portions which are not chamfered, and a ratio of a length L of the straight portion to a slit depth D is from 20 to 60%.