To easily form a flat ceiling surface wherein a ceiling part on which a luminaire is to be attached is prevented from protruding downward.

A ceiling structure is so constituted that a luminaire attaching member 5 attached a luminaire on its lower surface are arranged between ceiling joists 3, 30 and 3, 30 adjacent to each other in parallel with each other at predetermined intervals and for attaching a ceiling member on lower surfaces thereof. The luminaire attaching member 5 is provided with a luminaire attaching backing part 51 attached the luminaire on its lower surface, and an attaching part 60 attached on the ceiling joists (a pair) 31, 31 and for supporting the backing part 51. The attaching part 60 is so composed that the backing part 51 is supported so that a lower surface of the backing part 51 becomes a height position that is nearly equal to lower surfaces of the ceiling joists 31, 31.