A fixing device comprising: a cylindrical film; a heater contacting an inner surface of said film and including an electrode portion for supplying electric power to said heater, and a lubricant is applied in a region where said heater contacts said film; and a supporting member for supporting a surface of said heater opposite from a surface of said heater where said heater contacts said film; wherein an image on a recording material is heated by heat of said film and is fixed on the recording material, characterized by further comprising: a sealing member contacting a surface of said heater where said electrode portion of said heater is provided, said sealing member being provided at a position closer to a center of said heater than said electrode portion is, wherein said electrode portion is provided outside an end portion of said film with respect to a longitudinal direction of said film at an end portion of said heater with respect to a longitudinal direction of said heater, wherein the heater is a plate heater, wherein said sealing member includes an engaging portion engaging with an end portion of said supporting member with respect to a widthwise direction of said heater and a cantilever contact portion contacting the surface of said heater where said electrode portion is provided. a cylindrical film; a heater contacting an inner surface of said film and including an electrode portion for supplying electric power to said heater, and a lubricant is applied in a region where said heater contacts said film; and a supporting member for supporting a surface of said heater opposite from a surface of said heater where said heater contacts said film; wherein an image on a recording material is heated by heat of said film and is fixed on the recording material, characterized by further comprising: a sealing member contacting a surface of said heater where said electrode portion of said heater is provided, said sealing member being provided at a position closer to a center of said heater than said electrode portion is, wherein said electrode portion is provided outside an end portion of said film with respect to a longitudinal direction of said film at an end portion of said heater with respect to a longitudinal direction of said heater, wherein the heater is a plate heater, wherein said sealing member includes an engaging portion engaging with an end portion of said supporting member with respect to a widthwise direction of said heater and a cantilever contact portion contacting the surface of said heater where said electrode portion is provided. a sealing member contacting a surface of said heater where said electrode portion of said heater is provided, said sealing member being provided at a position closer to a center of said heater than said electrode portion is, wherein said electrode portion is provided outside an end portion of said film with respect to a longitudinal direction of said film at an end portion of said heater with respect to a longitudinal direction of said heater, wherein the heater is a plate heater, wherein said sealing member includes an engaging portion engaging with an end portion of said supporting member with respect to a widthwise direction of said heater and a cantilever contact portion contacting the surface of said heater where said electrode portion is provided.