PURPOSE: To obviate the necessity of dismantling and removing after placing concrete, and improve the execution performance and economic efficiency by forming a part of a concrete wall after placing concrete.

CONSTITUTION: A mold frame unit in placing concrete consists of a flat plate 1 made of concrete, supporting mold member 2 for supporting the lower end part of the flat plate 1, and a connecting member 3 for connection-supporting the contiguous flat plates made of concrete in the upper part of the supporting mold member 2. The supporting member 2 has a pair of opposed nipping-holding parts 21 and 22 on the obverse and reverse surfaces of the flat plate 1 made of concrete, and the flat plate 1 made of concrete is supported at the lower end part by a bottom plate part 23 and the nipping-holding parts 21 and 22. Further, the contiguous flat plates made of concrete are connection-supported by the connecting member 3. The concrete is left in a placed state free from the dismantlement after placing the concrete.