A thin keyboard depressing structure includes a circuit board and a frame. The circuit board includes a plurality of trigger portions each can be triggered to generate a keyboard signal. The frame is stacked over the circuit board and forms an outer frame, a plurality of inner frames and a plurality of keycaps in an integrated manner. The outer frame has a plurality of holding zones corresponding to the trigger portions. Each keycap is held in one holding zone corresponding to one trigger portion. The outer frame and the keycap are bridged by one inner frame. Each inner frame has at least two first connecting portions connected to the outer frame and at least two second connecting portions connected to the keycap. Each first connecting portion and each second connecting portion are bridged by a support portion.