Fixing device including heating roller and image forming apparatus

A fixing device comprising:

• a rotatable cylindrical heating roller,
• a heat source arranged in a hollow inner space of the heating roller, and
• a pressing roller pressed against the heating roller to form a fixing nip through which a sheet is passed in a sheet passing direction,
• wherein the heating roller has
• a substrate layer formed such that both end portions in a width direction perpendicular to the sheet passing direction are made thinner than a center portion in the width direction, within a sheet passing area through which the sheet is passed, and
• a heat conductive layer provided around an outer circumferential face of the substrate layer and having a heat conductivity higher than the substrate layer, and
• the substrate layer is thicker at non-sheet passing areas on both outer sides of the sheet passing area in the width direction than at both end portions of the sheet passing area in the width direction.