To provide a high speed electron beam diffraction device capable of exactly controlling epitaxial growth of a thin film in a wide range or a plurality of areas by a molecular layer unit and performing the monitoring by making an electron beam incident at an arbitrary angle and scanning with the electron beam in parallel.

This device is provided with an electron gun 12, first deflecting coils 14, 14 deflecting an electron beam generated from this electron gun 12 in the x-y direction and second deflecting coils 15, 15 adjusting the deflected electron beam at an arbitrary angle and particularly making the electron beam parallel. In this case, the electron beam is made incident on a sample 16 at an arbitrary angle, is scanned in parallel, is reflected and is hit against a screen 18, and mirror reflecting intensity is detected by a charge coupled device 19.