Provided is a mix weighing device which facilitates a constant mixing ratio, in terms of external appearance, of a plurality of types of materials after mix weighing. This mix weighing device (1) is a device to mix-weigh a plurality of types of the material on the basis of individual weighed target weight (Wt), wherein the mix weighing device (1) is provided with a conveying unit (10), a mix weighing unit (20), a storage unit (61), a weighed target weight setting unit (66), and a control unit (60). The conveying unit (10) conveys the material. The mix weighing unit (20) weighs and discharges the material. The storage unit (61) stores the apparent specific gravity and a mix volume proportion (Pv) of each type of material. The weighed target weight setting unit (66) sets individual weighed target weight (Wt) for each type of the material on the basis of the apparent specific gravity and the mix volume proportion (Pv). The control unit (60) controls the conveying unit (10) and the mix weighing unit (20) on the basis of the individual weighed target weight (Wt).