A device for forming foamed kneaded material and a method for forming foamed kneaded material are obtained capable of filling a pattern forming space of a mold with foamed kneaded material in a well foamed condition. First, a supply device supplies a foamed kneaded material (a) into a cylinder (20) (first process). Then, in a state in which an internal space (22) of the cylinder (20) is communicated with a pattern forming space (14) of a mold (12), the piston (26) disposed in the cylinder (20) is moved toward the foamed kneaded material (a) side while opening a gas release hole (40A) formed piercing through the piston (26) (second process). Then, at a timing when the piston (26) has reached an expected position (X) where the piston (26) is expected to be on contacting the foamed kneaded material (a) supplied into the cylinder (20), the gas release hole (40A) is closed by an open-close plug (40B) (third process). Then, the foamed kneaded material (a) supplied into the cylinder (20) is pressed toward the pattern forming space (14) side of the mold (12) by moving the piston (26) toward the foamed kneaded material (a) side (fourth process).