PURPOSE: To enable playing games whether it rains or the sun is shining and even in winter by supporting roofing with arched steel bars, covering the upper side of a gate ball field with the roofing, anchoring the legs of the steel bars to a foundation at both sides of the gate ball field, and allowing good ventilation through the open ends of the installation of the roofing.

CONSTITUTION: A plurality of arched steel bars 1 spanning a gate ball field are arranged parallel to one another, with their legs anchored to a foundation 3. Roofing is put over the steel bars to form a canopy 4. Either the canopy 4 is opened at its ends or an openable ventilation window is provided. Thus the structure is simplified, construction work can be achieved easily in a short construction period, and various events can be held.