An optical element in which transmittance of light monotonically decreases from a center portion toward a peripheral portion, the optical element includes an absorbing material portion made of a material that absorbs a part of light and formed such that its thickness monotonically increases from the center portion toward the peripheral portion; and a transparent material portion made of a material that transmits light and is stacked on the absorbing material portion, a total thickness of the absorbing material portion and the transparent material portion being substantially constant.