A combined winding structure is provided. The combined winding structure includes a plurality of winding wires each having a winding portion in a hollow column form, an anodic portion and a cathodic portion; the anodic portions and the cathodic portions are integrally extended from the winding portions respectively. The winding portions each have a surrounding dimension, and the surrounding dimensions are mutually different. The winding portion with the smaller surrounding dimension is located inside and surrounded by the winding portion with the larger surrounding dimension. With these arrangements, the combined winding structure can have a larger equivalent cross-sectional area and lower production costs. A magnetic device is also provided, which includes the aforesaid combined winding structure.