The invention provides an optical device, including a light-transmitting substrate, optical means for coupling light into the substrate by total internal reflection, and a plurality of partially reflecting surfaces carried by the substrate, characterized in that the partially reflecting surfaces are parallel to each other and are not parallel to any of the edges of the substrate. Condition indicators are associated with each roadway and bridge, and costs involved with first repairing each bridge and roadway at different points in time considering the condition indicators are determined and compared. The tests preferably include heart rate variability, differential ECG, omega brain wave, jump and stimulus response tests. The thickness of the IDT electrode is in a range of about 6. The pushing member 51 is brought into contact with a back part of a wafer W with respect to a direction in which the wafer W is moved to move the wafer W in a direction toward the cooling plate 3 in which the flotation gas is spouted.