To easily place the concrete during the execution, and to generate of cracks with difficulty by providing an arc-shaped corner part of a frame provided on an upper end of a prismatic box in which pipes to be connected to an underground tank are stored.

A riser part of a pipe is surrounded by a prismatic box, a frame 20 is provided on an upper end of the box, and a lid body 30 is engaged with the frame 20 to form a man hole. During the execution, a box is placed on a buried underground tank, a horizontal pipe of each piping placed through a hole is connected to a riser pipe from the underground tank, and the periphery of the box is fixed by placing the concrete. A box engagement part is placed so as to meet the upper end of the box, and the concrete 8 is placed thereon. Because a corner part 28 of the frame 20 is arc-shaped, the flow of the concrete 8 is improved to facilitate the flow, and cracks are difficult to generate even in the elapse of time.