To provide a hopper for feeding raw materials to be mixed which is capable of feeding and mixing a fixed amount of auxiliary raw materials in the hopper at the same time where chief raw materials have already been fed and stored.

In feeding chief raw materials and auxiliary raw materials via a hopper for feeding raw materials which is connected with and penetrated into a tubular body 5 having kneading/delivering screw 51 built-in so that may be free to rotate, a flow distribution is exhibited within the hopper due to the difference of flow of the chief raw materials (s1) occurred in a connecting and penetrating parts by driving the kneading/delivering screw 51. The flow at the area of the late flow among the flow distribution is compulsorily stopped by flapping a flapper (2) which is installed within the hopper 1, and the chief raw materials s1 at the area of the fast flow is caused to flow down fast and then the auxiliary raw materials s2 is fed thereto.