PURPOSE: To heighten antiplane rigidity of precast concrete (PC) panel and to improve bonding strength of concrete by providing ribs in checkerboard layout over the surface of a flat member of the PC panel with sheaths embedded in the flat member and by installing tendons therein.

CONSTITUTION: At the surface of a flat member 22 of a precast concrete (PC) panel 21, ribs 23 are provided upwardly protruding in checkerboard layout and at the inside of the flat member 22, a number of sheaths 24 are embedded in parallel with the ribs 23 and in checkerboard layout. The PC panel is then set at a position where a floor board is to be constructed, and concrete is placed over the flat member 22 and the ribs 23, using the PC panel as a form for concrete placing. At the same time, tendons are installed at the inside of the sheaths 24. Thereby antiplane rigidity of the PC panel can be heightened without making the panel a heavyweight structure, while reduction of shorting, shortening of term of works and saving of manpower are enabled.