First, a supply device supplies a foamed kneaded material into a cylinder. Then, in a state in which an internal space of the cylinder is communicated with a pattern forming space of a mold, the piston disposed in the cylinder is moved toward the foamed kneaded material side while opening a gas release hole formed piercing through the piston. Then, at a timing when the piston has reached an expected position where the piston is expected to be on contacting the foamed kneaded material supplied into the cylinder, the gas release hole is closed by an open-close plug. Then, the foamed kneaded material supplied into the cylinder is pressed toward the pattern forming space side of the mold by moving the piston toward the foamed kneaded material side.