A first pipe 231 and a second pipe 232 are connected using connectors 233 and 234 so that at least one of the connectors 233 and 234 is located in a through-hole 133. In this way, since the through-hole 133 is filled in by at least one of the connectors 233 and 234, the gap between the connectors 233 and 234 and the edge of the through-hole 133 can be considerably reduced. It is, therefore, possible to prevent hot air from moving to the front of a panel 100 through the gap between connectors 233 and 234 and the edge of the through-hole 133.