We have developed aninsituTEM/PL apparatus, which enables us to excite PL emissions from a microscopic area of a specimen inside a TEM. The microscopical area of 20 &mgr;m can be examined by TEM, PL, and CL methods under the same experimental conditions. The apparatus may be applied to a transmission electron microscope of side‐entry type with a minor modification. The apparatus is extremely useful for microscopic characterization of structural and electronic properties in an inhomogeneous material. Utilizing the apparatus, we have examined the spatial distribution of extended defects and point‐defect complexes in CVD diamond. The apparatus will be utilized to study the structural and optical properties of materials under electron irradiation. ©1995 American Institute of Physics.