A sheet feeder includes a sheet feeding cassette stored in a cassette storage part, a heater and flow regulating plates. A first gap is formed between the bottom plate of the sheet feeding cassette and a bottom portion of the cassette storage part, and having an air intake port. A second gap is formed between the side plate of the sheet feeding cassette and a side portion of the cassette storage part and has a vent port communicating with the first gap and the sheet storing part. The flow regulating plates are disposed in the first gap so as to form a duct together with the sheet feeding cassette and the cassette storage part. Air flow is generated such that air is supplied from the air intake port into the first gap, is heated, rises through the second gap from the vent port, and flows to the sheet storing part.