To provide an envelope for an image display device, a hermetic sealing material and a sealing method, with which sealing is possible at a temperature less than 400° C., sufficient strength is achieved in a high temperature environment, and characteristics will not decrease under high humidity conditions including a high temperature and high humidity atmosphere. An envelope for an image display device, having envelope-constituting members including an image display portion made of glass, sealed with a hermetic sealing material layer, wherein the hermetic sealing material layer includes an organic hermetic sealing material layer obtained by firing an organic hermetic sealing material preferably including a primer layer, a fired body of the organic hermetic sealing material has a viscosity of at least 105 Pa·s within a range of from 200 to 350° C., and preferably the flexural strength after the fired body is left at rest in a constant temperature and constant humidity atmosphere at a temperature of 80° C. in a humidity of 85% for 7 days is at least 90% of the flexural strength before the still standing.