A driving fan device has a transmission device and multiple blade assemblies. The transmission device has a transmission seat disposed at a center of the transmission device. The blade assemblies are mounted on the transmission seat. Each one of the blade assemblies has a fixing portion and a tilting portion. The fixing portion is mounted radially on the transmission seat and has a pivotal end and a groove. The pivotal end is disposed away from the transmission seat. The groove is caved inwardly near the pivotal end and has an inner surface. The tilting portion is pivotally connected to the fixing portion and has a rotating part and a forced part. The rotating part is disposed at the tilting portion, is pivotally connected to the pivotal end of the fixing portion, and has an abutting surface corresponding to the inner surface. The forced part is connected to the rotating part.