PURPOSE: To constitute the device so that the upper end part of a wall body is covered in good style, and also, a mailbox can be fixed simply by adjusting its position.

CONSTITUTION: In the upper end part of a wall body 1, a coping-like rail material 2 is bonded and fixed along the longitudinal direction, and in the bottom part of a mailbox 3, a recessed groove part 4 opened downward is formed, and the recessed groove part 4 is engaged to the coping-like rail material 2 so as to be freely slidable in the longitudinal direction, and the mailbox 3 is provided so as to be movable along the coping-like rail material 2, and also, the mailbox 3 is fixed to a suitable position of the coping-like rail material 2.