The device (1) for adjusting the degree of mixing according to the present invention is installed in mixing equipment (2) equipped with a kneading/mixing screw (4) for mixing material while feeding the material to a downstream side, wherein a gate member (13) is moved relative to a portion (12) of a circular section provided for the kneading/mixing screw so as to cause a change in the area of a flow path formed between the gate member and the portion of a circular section, thereby adjusting the degree of mixing of the material. Drive quantity changing means (16) is disposed between the gate member and drive means (15). The drive quantity changing means is constructed so as to change the drive quantity, x, into the movement quantity, Δδ, in accordance with a profile such that a change rate of the movement quantity, Δδ, relative to the drive quantity, x, is made smaller when the degree of opening, δ, of the gate member is smaller and the change rage of the movement quantity, Δδ, relative to the drive quantity, x, is made larger when the degree of opening, δ, of the gate member is larger. Through such construction, it is possible to let the degree of mixing change at a constant change rate relative to the drive quantity of the drive means.