Mixing device for mixing particulate materials, preferably for producing a dry building material mixture, in particular a plaster mortar, in discontinuous and/or batchwise operation, with a preferably one-piece mixing container for receiving the materials, wherein the mixing container has an upper container upper part with at least one inlet means for introducing the materials into the mixing container along a filling direction which is preferably predetermined by gravity, and a lower container part with at least one outlet means for discharging mixed materials from the mixing container, wherein the lower container part is substantially arcuate in a sectional plane extending orthogonally to a longitudinal axis of the mixing container, and with a mixing shaft which is arranged rotatably about a mixing axis within the mixing container, wherein mixing tools, which are preferably axially spaced apart, are arranged on the mixing shaft and are drivable within the mixing container with the rotation of the mixing shaft about the mixing axis in a working direction for mixing the materials to form mixed products, wherein the upper container part, in a sectional plane extending orthogonally to the longitudinal axis of the mixing container, is substantially U-shaped with two legs (11, 12) directed towards the lower container part, wherein, within the mixing container, the inner leg surfaces (13, 14) of the legs (11, 12) and the inner bottom surface of the lower container part merge substantially tangentially into one another, wherein the upper container part comprises two or more inlet means for introducing the materials into the mixing container, and wherein the inlet means are each arranged in the region of an axial end (17, 18) of the mixing vessel, characterized in that the outlet means is arranged in the region of a center point of the lower container part, and that the mixing tools of the mixing shaft are designed and/or arranged within the mixing container in such a way that the materials can be conveyed within the mixing container in opposite axial conveying directions (X 1, X 2), it being possible for the materials to be conveyed, starting from the axial ends (17, 18) of the mixing container, towards the outlet means of the mixing container. with a preferably one-piece mixing container for receiving the materials, wherein the mixing container has an upper container upper part with at least one inlet means for introducing the materials into the mixing container along a filling direction which is preferably predetermined by gravity, and a lower container part with at least one outlet means for discharging mixed materials from the mixing container, wherein the lower container part is substantially arcuate in a sectional plane extending orthogonally to a longitudinal axis of the mixing container, and with a mixing shaft which is arranged rotatably about a mixing axis within the mixing container, wherein mixing tools, which are preferably axially spaced apart, are arranged on the mixing shaft and are drivable within the mixing container with the rotation of the mixing shaft about the mixing axis in a working direction for mixing the materials to form mixed products, wherein the upper container part, in a sectional plane extending orthogonally to the longitudinal axis of the mixing container, is substantially U-shaped with two legs (11, 12) directed towards the lower container part, wherein, within the mixing container, the inner leg surfaces (13, 14) of the legs (11, 12) and the inner bottom surface of the lower container part merge substantially tangentially into one another, wherein the upper container part comprises two or more inlet means for introducing the materials into the mixing container, and wherein the inlet means are each arranged in the region of an axial end (17, 18) of the mixing vessel, characterized in that the outlet means is arranged in the region of a center point of the lower container part, and that the mixing tools of the mixing shaft are designed and/or arranged within the mixing container in such a way that the materials can be conveyed within the mixing container in opposite axial conveying directions (X 1, X 2), it being possible for the materials to be conveyed, starting from the axial ends (17, 18) of the mixing container, towards the outlet means of the mixing container.