To facilitate construction work of a sealing material even when a space between a vertical frame comprising a frame body of a fixedly compacted panel and a stile of an opening/closing sliding door is narrowed.

The vertical frame 2C on which the panel is mounted in a permanently fixing manner, and a vertical frame 2A to which the opening/closing sliding door 11 is fitted are joined to each other. A width of the vertical frame 2A in a direction of going in and out is smaller than that of the vertical frame 2C. The sealing material 15 is applied to the joint part of the vertical frames from an exterior side. The stile of the opening/closing sliding door 11 is divided into an interior-side stile 24 and an exterior-side stile 25. An attachment 26 is pivotally fitted to the interior-side stile 24 in a horizontally rotatable manner. A front end of the attachment 26 is fitted into a channel 25c of the exterior-side stile 25 to compress an elastic material 27 in the channel 25c. In this state, an engaging part 25a of the exterior-side stile 25 is engaged with a projection 24b of the interior-side stile 24. A sealing material 29 is interposed between a part 25d of the exterior-side stile 25 facing a panel face, and the panel 1A.