A lens assembly made of porous ceramic is provided with concave sections (K1,K2) into which an adhesive for fixing lenses (L3,L4) inserted into a lens frame (10B) is injected. Each of the concave sections has an outward opening and a spacing wall provided between a hollow part (100) of the lens frame and the opening. The adhesive injected into the concave sections (K1,K2) passes through multiple pores in the lens frame (10B) made of porous ceramic, and reaches the periphery of each of the lenses (L3,L4), thereby fixing the lenses (L3,L4) to an inner wall of the hollow part of the lens frame (10B).