A die for forming a honeycomb structure, comprising: a second plate-shaped portion having a second bonded surface, where a back hole for introducing a forming raw material is formed; and a first plate-shaped portion that has a first bonded surface and is formed of tungsten carbide based cemented carbide, where a cavity communicating with the back hole is formed in the first bonded surface side, and a slit communicating with the cavity to form a forming raw material is formed, wherein the second plate-shaped portion is formed of a material containing at least one selected from a group consisting of iron, steel, aluminum alloy, copper alloy, titanium alloy, and nickel alloy, the first plate-shaped portion is arranged on the second plate-shaped portion such that the first bonded surface comes into contact with the second bonded surface, an open end of the cavity on the first bonded surface has a diameter different from that of an open end of the back hole on the second bonded surface and a bottom portion as a head edge of the cavity has a flat shape on a cross section perpendicular to a top surface of the first plate-shaped portion at an end opposite to the open end of the cavity such that the flat shape of the bottom portion extends to the cavity sidewall and is parallel to the first bonded surface of the first plate-shaped portion, and the open end of the cavity on the first bonded surface is arranged inside the open end of the back hole on the second bonded surface; wherein the diameter (D 1) of the open end of the back hole on the second bonded surface is larger than the diameter (d 1) of the open end of the cavity on the first bonded surface, and the diameter of the open end of the back hole on the second bonded surface is 1.01 to 1.50 times of the diameter of the open end of the cavity on the first bonded surface. a second plate-shaped portion having a second bonded surface, where a back hole for introducing a forming raw material is formed; and a first plate-shaped portion that has a first bonded surface and is formed of tungsten carbide based cemented carbide, where a cavity communicating with the back hole is formed in the first bonded surface side, and a slit communicating with the cavity to form a forming raw material is formed, wherein the second plate-shaped portion is formed of a material containing at least one selected from a group consisting of iron, steel, aluminum alloy, copper alloy, titanium alloy, and nickel alloy, the first plate-shaped portion is arranged on the second plate-shaped portion such that the first bonded surface comes into contact with the second bonded surface, an open end of the cavity on the first bonded surface has a diameter different from that of an open end of the back hole on the second bonded surface and a bottom portion as a head edge of the cavity has a flat shape on a cross section perpendicular to a top surface of the first plate-shaped portion at an end opposite to the open end of the cavity such that the flat shape of the bottom portion extends to the cavity sidewall and is parallel to the first bonded surface of the first plate-shaped portion, and the open end of the cavity on the first bonded surface is arranged inside the open end of the back hole on the second bonded surface; wherein the diameter (D 1) of the open end of the back hole on the second bonded surface is larger than the diameter (d 1) of the open end of the cavity on the first bonded surface, and the diameter of the open end of the back hole on the second bonded surface is 1.01 to 1.50 times of the diameter of the open end of the cavity on the first bonded surface.