A dust filter unit for a canister is provided. An inlet port and an outlet port are formed in a housing and opening into the atmosphere. A communication port is formed in the housing and leading to the canister. A filter is arranged within the housing at a location between the inlet port and the output port. A first one-way valve is arranged within the housing at a location between the communication port and the outlet port, for allowing evaporative fuel to flow from the communication port to the outlet port. A second one-way valve is arranged within the housing at a location between the filter and the communication port, for allowing fresh air to flow from the filter to the communication port. Thus, the inlet port, outlet port, communication port, and first and second one-way valves are all provided in one piece within the housing.