To provide an optical unit and an optical device, in which a deterioration of surface precision of the effective optical surface of optical elements, dew condensation, or the like is hardly generated even when a space enclosed by a first optical element and a second optical element exists.

The optical unit in which the first optical element which has the effective optical surface and the second optical element which has the effective optical surface are integrated into one body, is provided with at least the space enclosed by the effective optical surface of the first optical element and the effective optical surface of the second optical element, and a gas passage through which gas flows between the space and outdoor air.