An image forming device includes an exposure device configured to emit exposure light and an air flow generator configured to generate an air flow. The exposure device includes a heat source that generates heat and a heat sink configured to dissipate the heat. The heat sink includes a plurality of fins located inside the air flow. The plurality of fins extend in a direction parallel to a direction where the air flow flows and are arrayed in a direction orthogonal to the direction where the air flow flows. The plurality of fins are formed so as to increase in height from an upstream side toward a downstream side in the direction where the air flow flows.