The present invention aims to evenly and surely knead a concrete material comprising less water amount. Concrete material layer entered into a kneading tank is cut in an up-and-down direction and divided into a plurality of layer sections arrayed side by side along a right-and-left direction,, and one of the divided layer sections is piled up another one of the divided layer sections in the up-and-down direction, then the piled up concrete layer sections are compacted, in other words are pressed in the up-and-down direction and extended in a horizontal direction, and further these steps are repeated.