To dispense with a high-rigidity section in a lower frame by providing a bay window comprising a hook frame having an engaging part engaged with a vertical frame projecting part at one end and a bent grip part at the other end, and a lower frame having plural setting blocks.

A bay window M is formed by a hook frame 5 having an engaging part 51 engaged with a vertical frame projecting part 1 at one end and a bent grip part 52 at the other end, and a lower frame 4 having setting blocks 32, 33. Subsequently, when the engaging part 51 is engaged with a projecting part 1 of a vertical frame 2, and one end of the lower frame 4 is placed on a bracket B, in the bay window M, the total load is worked as angular moment by the pulling effect of the hook frame 5 to be applied to a pressure receiving block 31 of the vertical frame 2. Secondly, the vertical load of the glass G is applied to the setting block 32 and transmitted to the vertical frame 2 through the pressure receiving block 31 and the bracket B. Thus, rational load transmission is performed to dispense with a high-rigidity section in the lower frame 4.