An electron microscope is offered which can facilitate adjusting a monochromator. The electron microscope (100) includes the monochromator (20) having an energy filter (22) for dispersing the beam (EB) according to energy and a slit plate (24) disposed on an energy dispersive plane. The slit plate (24) is provided with plural energy-selecting slits (25) which are different in width taken in a direction where the beam (EB) is dispersed. The microscope (100) further includes a lens system (30) on which the beam impinges after being monochromatized by the monochromator (20), a first measuring section (50) for measuring the intensity of the beam (EB) emitted from an electron beam source (10), a second measuring section (60) for measuring the intensity of the beam (EB) that has passed through an active one (25-L) of the energy-selecting slits (25), and a slit identifying portion (72) for identifying the active energy-selecting slit (25-L) from the plural energy-selecting slits (25) on the basis of the results of measurements made by the first and second measuring sections (50, 60).