To achieve highly reliable sealing processing without reducing productivity and being affected by a water painting processing condition temperature caused by water painting processing.

A sealing device includes: a tip pressing unit 5d provided at a carrying-in side end of an envelope formed by containing contents in an envelope form, and applying water by pressing a re-moistening paste portion of the envelope against a water application member 5a; a pasting sheet metal 5b provided at a regulation position side of the envelope to be carried in and provided with a tip warming unit 5e for warming a water application member 5a; a water application processing unit 5 having a heater 5f for heating the tip warming part 5e in a predetermined temperature; a temperature detection unit 6 for outputting a water application processing condition temperature being a condition temperature when selecting a control mode of the water application processing as water application processing condition temperature information;and a control unit 9 for determining whether the water application processing condition temperature detected by the temperature detection unit 6 is an ordinary temperature or a low temperature to the re-moistening paste and controlling the water application processing unit 5 by a control mode selected according to the temperature obtained from the determination results.