A dust filter of an evaporated fuel treatment device is taught that preferably include a filtration member for filtering air introduced to an atmosphere introduction path, and a casing receiving the filtration member therein. The dust filter being disposed on the atmosphere introduction path of the evaporated fuel treatment device. The filtration member has an arcuate shape in cross section, and wherein the filtration member is arranged and structured such that air flows in a radial direction thereof, so as to be filtered.