An adapter device for adding ink to a whiteboard marker is provided with a filling unit and a fixing unit. The fixing unit is provided with two clamping elements. The connection ends of both the clamping elements are connected to a filling body of the filling unit pivotally. When a whiteboard marker is clamped in the clamping space between both the clamping elements, an inserted body of the filling unit is directly inserted into a refill of the whiteboard marker, so that the ink is directly added into the refill of the whiteboard marker through the filling body of the filling unit, and thus the adding process of the ink is simplified. The size of the clamping space formed between both the clamping elements fixed to the filling unit can be adjusted, so that the effect that the whole adapter device for adding the ink to the whiteboard marker can be combined with the whiteboard marker effectively is ensured, the condition of falling of the whiteboard marker in the ink adding process is prevented, and thus the adapter device for adding the ink to the whiteboard marker can be suitable for whiteboard markers with various specifications.