To construct concrete forms for a veranda, an open corridor, and the like of an apartment house or the like efficiently at a low cost.

A panel unit is composed of a square exterior wall panel 1; a floor face panel 106 pivotally supported to the lower edge of the exterior wall panel 1 so as to be movable; lateral exterior wall panels 80, 82 connected at a right angle to both side parts of the exterior wall panel 1; and an interior wall panel supported to the exterior wall panel 1 so as to be opposed with a specified space to the exterior wall panel 1. After placing concrete, the panel unit is moved to the upper floor of a concrete building by a lifting device such as a crane, and a concrete form for forming an open corridor or the like at the upper floor is constructed by the panel unit. After concrete placing is completed, the panel unit is lifted again to construct concrete forms in order at every floor.