1. ABSTRACTThis report details our development of a smoothly curved inner lens for use in automotive signalling lamps. Such a lens allows for greater freedom at the design stage of an automobile, and it can be useful for economizing on space.Until recently, however, the design of such lenses has been in difficulty due to the complex geometries involved, and the appearance and light distribution has often turned out to be inferior to that of conventional plane and spherical lenses. The main reason for this is that in the case of these conventional lenses, optical calculations can be reduced to simple equations, but this is generally not possible with smoothly curved lenses.Our goal has been to develop a smoothly curved inner lens whose optical characteristics could be calculated and verified. This development project can be divided into three stages: design, processing, and evaluation. We are currently developing the third stage. This report explains the procedure by which the surface characteristics of the lens are calculated, and offers some concrete examples of this procedure applied.