A fan includes a casing that is composed of a front cover and a rear cover, a base mounted under the casing, and blades rotatably mounted in the casing. The base includes support frames symmetrically mounted thereto. The front and rear covers are each composed of a plurality of circular frames of different diameters. The rear cover has a lower portion that forms slots corresponding to the support frames so that the support frames are movably received through the slots respectively. A connection bar is connected to the rear cover so that the casing may undergo vertical and horizontal rotations through the arrangement of the slots for adjusting direction of airstream generated by the fan, thereby realizing an effect of indoor air circulation. Further, due to the arrangement of the rotation structure inside the casing, the outside appearance of the fan shows a sense of completeness of aesthetics.