[Problem] To provide with a simple constitution a device and method whereby it is possible to smoothen, in a mixing tank, the surface of mixed material to be pressed by a filling device and thereby precisely form a mold. [Solution] A mold-making device is provided with: a mixing device (3) that is provided with a mixing tank (1) and mixing fins (2) and mixes a particle-like aggregate and additives to form a mixed material (M); a mold (4) for forming the mixed material (M) in a prescribed shape; and a filling device (5) that presses the surface of the mixed material (M) inside the mixing tank (1) to fill the mold (4) with mixed material (M). The mixing fins (2) have a lattice like constitution by means of a plurality of horizontal members (21) and a plurality of vertical members (22). The tip of a rotating drive shaft (23) is bonded to the upper edge of the mixing fins (2), and the constitution is such that the rotating drive shaft (23) will not be immersed in the mixed material (M). Scrapers (29) for levelling the surface of the mixed material (M) are provided on the lower parts of the mixing fins (2).
