A kneading state detection device includes an acquisition unit that, when an extrusion molding machine that kneads a raw material or kneads a raw material and an additive is in operation, acquires an output of an AE sensor installed on a housing of the extrusion molding machine, and a determination unit that determines a kneading state of the raw material, based on a comparison between a change in intensity of the output of the AE sensor acquired by the acquisition unit and a threshold.