A transmission electron microscope for irradiating a specimen with an electron beam, wherein the electron beam passed through the specimen is imaged on an imaging screen by a magnifying lens system. The electron microscope includes a deflector for deflecting the electron beam to thereby scan a specimen with the electron beam, and a memory for storing a range within which the specimen is to be preliminarily scanned with the electron beams and the number of scans to be performed. The specimen is preliminarily scanned with the electron beam within the preliminary scan range for the number of times on the basis of the corresponding data read out from the memory.