PURPOSE: To contact-bond a PCa concrete wall post single board and raise joint performance and reliability and thereby enhance workability by adding the force of prestress produced by engagement joining of an uneven cotter and a PC steel rod.

CONSTITUTION: Uneven cotter-attached side surface joint units 3, 13 and 23 of PCa concrete wall post single boards 1, 11 and 21 where reinforcing bars 2, 2a and 2b are buried crosswise, are engaged with uneven cotter-attached end face joint units 7, 17 and 27 of other PCa concrete wall post single boards 5, 15 and 25 while reinforcing bars 6, 6a and 6b are buried and placed in contact with each other so that grout G may be filled up therein. A PC steel material 9 is inserted into a series of insertion sheaths 4, 14, 24, 8, 18 and 28 continuously installed to the side surface joint units and the end face joint units of both the PCa concrete wall post single boards and stretched and fixed with 9a and contact-bonded and jointed so that they may be transverses cross-shaped, T-shaped or L-shaped respectively.