A fixing device includes a first radiating portion that includes plural light sources arranged along a first direction at a determined interval, and radiates light on a recording medium on which a toner image is formed and which is transported in a second direction intersecting with the first direction, and an optical member that includes plural transmission regions through which the light radiated by the plural light sources is transmitted and includes plural light diffusion portions diffusing the light in the first direction on each of the plural transmission regions.