An extrusion forming apparatus includes an extruding section, a chamber drum, and a forming section. The extruding section kneads a material including a ceramic raw material and extrudes a kneaded material. The chamber drum has a first space portion having a first extruding direction extending portion through which the kneaded material is allowed to flow in an extruding direction, and a second space portion which has a second extruding direction extending portion extending in the extruding direction and a direction changing portion bending from the extruding direction to a downward direction, to allow the kneaded material to flow in the downward direction changed from the extruding direction. The second space portion has a cross section obtained by isotropically decreasing a cross section of the first space portion perpendicular to a flow-through direction of the kneaded material. The forming section has a die to extrude a ceramic formed body.