The invention is to simplify operations performed when imaging an electron diffraction pattern by using a transmission electron microscope. As a solution to the problem, a transmission electron microscope includes a detector to which an electron diffraction pattern is projected, a mask for zero-order wave configured to be inserted into and pulled out from between a sample and the detector, and a current detector configured to be inserted into and pulled out from a detection region of the zero-order waves in a state where the mask is inserted. An amount of current of electron beams emitted to the mask is measured in real time, and the measurement result is automatically reflected in settings of imaging conditions of an imaging camera provided in the transmission electron microscope.