A fan device includes: a fan housing configured with a receiving space defined among opposite top and bottom walls, and a surrounding side wall; and a fan impeller mounted in the receiving space, disposed adjacent to an air outlet in the top wall and operable to rotate about a central axis transverse to the top and bottom walls of the fan housing. The fan impeller includes a hub body disposed coaxially with the central axis, and a plurality of angularly spaced apart fan blades extending outwardly and radially from the hub body. An angular distance between each adjacent pair of the fan blades is different from that of any other adjacent pair of the fan blades.