An exposure device, which emits light according to a gray level of image data, includes plural light emitting element lines arranged at different positions in a sub scanning direction, a number of the light emitting element lines being a number of bits representing a number of gray levels. Each of the light emitting element lines includes plural light emitting elements arranged in a line in a direction parallel to a main scanning direction, the light emitting elements numbers of layers of organic electro-luminescence light emitting elements being the same. The numbers of layers of the organic electro-luminescence light emitting elements laminated in the light emitting element lines, which are arranged at different positions in the sub scanning direction, are different from each other.