To provide a lubricant for hot plastic working which is excellent in lubricating properties, feedability and operability and will produce no adverse affects on the corrosion resistance of the products. The method includes the steps of: forming a lens-shaped curve at a surface side of a transparent substrate; forming an inorganic material film on the transparent substrate so as to bury the curve therewith; and planarizing the surface of the inorganic material film to provide a microlens where the curve is buried with the inorganic material film. Strategy outputs can be sent to a vehicle system controller andor a power assist gauge. The ram head bears under the effect of the compression spring against a control surface of the drive shaft. Each waveguide has laminated core layers which are formed of materials of different refractive indexes.