PURPOSE: To improve workability with a round edge having uniform quality and allowing mass production.

CONSTITUTION: A joiner 4 is fitted to a reentrant part 3 where a ceiling 1 and a wall face 2 meet with a screw 8 and the like, and a round edge 6 is coupled and fitted to the joiner 4. The upper fitted section 40 of the round edge 6 is inserted between the upper fitting section 40 of the joiner 4 and the ceiling 1 to be coupled and fitted to the upper fitting section 40, and the lower fitted section 65 of the round edge 6 is coupled and fitted to a lower fitting section 45 provided nearer to the wall face 2 than the upper fitting section 40 of the joiner 4. The joiner 4 can be simply fitted, and the round edge can be simply fitted to the joiner 4 by an unskilled person. The joiner 4 and the round edge 6 have uniform quality and are made of resin allowing mass production, the production cost is reduced, and quality control can be easily made.