Abstract: Each of divided surfaces or regions of a reflector and its adjoining divided surface are continuous with each other by a continuous surface, and a diffusion surface for diffusing light is formed at the boundary portion between the divided surface and the continuous surface. Even when the light from a bulb does not reach the continuous surface, the light, diffused by the diffusion surface, covers the region of the continuous surface, thereby preventing this region from forming a stripe-like dim illuminating portion. A gently, convex-curved surface portion is formed at the boundary portion between the divided surface and the continuous surface, thereby further enhancing the light diffusion, and also preventing the stripe-like dim illuminating portion from being formed.