In a semiconductor-fabrication equipment of a minienvironment system, ambient air is prevented from entering a gap between an opening of the semiconductor-fabrication equipment and a wafer gateway of a hermetic container to prevent dust entrained in the ambient air from adhering to wafers in the hermetic container. The hearing aid may be programmed to successively select in a defined sequence a parameter set that defines at least one operating characteristic of the signal processing circuit from a group of such parameter sets. The mechanical venting assembly of this invention ensures that the vent openings associated therewith will not become plugged with debris. The number of the threads assigned to each of the first and second computing units is based on a number of processors associated with each of the first and second computing units and a per-processor performance of the first and second computing units. By such a constitution, an illumination optical device capable of enhancing image quality and addressing andor achieving miniaturization and a projector including the device can be provided.