An extrusion-forming device includes an extruding portion having a drum including a supply port through which a clay flows into the inside, a screw having a rotary shaft and a rotary blade and configured to convey the clay, and an extrusion port through which the clay is discharged; and a forming portion having a die provided with forming grooves. The device includes, as the screw on the side of the supply port, supply port side screws having two rotary blades and, as the screw on the side of the extrusion port, a extrusion port side screw having one rotary blade, and a ratio P/D is in a range of 0.5 to 0.9.