In a method of producing a test-sample for a transmission electron microscope, it is so arranged that a massive body in a rectangular parallelepiped shape including a multiple quantum well active layer is cut out from a laser diode being a workpiece; thereafter, a test-sample is produced in which tilting oblique cutoff portions are formed at corner portions contiguously bordering on an upper surface of the massive body, so that surface-part active layers can be visually identified thereat; and thereafter, the test-sample is made thinner, and also an observation test-sample is cut out therefrom by taking on, as references, two surface-part active layers visually identifiable at the tilting oblique cutoff portions.