To rapidly and easily carry out a construction work by forming a corridor slab lower than a floor slab and covering the upper face of the corridor slab with the corridor panel and forming a space for piping/wiring at the upper part of the corridor slab.

In an apartment house, when an indoor side floor slab (22) and a corridor side corridor slab (21) are formed of concrete, the corridor slab (21) is formed lower stepwise than the floor slab (22), the upper face of the corridor slab (21) is covered with the corridor panel (28) and the height of the corridor panel (28) is made substantially same with the upper face of the floor slab (22) and further, a space (30) for piping/wiring is formed between the corridor panel (28) and the corridor slab (21).