A lattice strain measuring method including the steps of: using a scanning transmission electron microscope 12 to apply convergent electron beams 34 to a sample 32 and obtain a convergent-beam electron diffraction image 36 of the sample 32; computing a lattice strain magnitude of the sample 32, based on the obtained convergent-beam electron diffraction image; and displaying the computed lattice strain magnitude, associated with an electron microscope image of the sample 32. A scanning transmission electron microscope 12 is used, whereby electron beams 34 are caused to scan to thereby suitably set an incidence position. Accordingly, the incidence position of the electron beams can be displaced at a nanometer-order pitch accurately in a short period of time. The use of a scanning transmission electron microscope 12 requires no image forming lens below the sample 32, and the convergent-beam electron diffraction image is free from the distortion due to the influence of an image forming lens. Thus, a distribution of lattice strains in an electronic device having, e.g., a micronized structure can be displayed in an image with high resolving power and with high accuracy and furthermore in a short period of time.