A path of a spin-polarized electron beam is split into two by a splitter. A spin direction of the spin-polarized electron beam is rotated by a spin direction rotator disposed on a first path, and delayed by a first delay device. On a second path, the electron beam passes through a sample stage. The spin-polarized electron beams split into the first path and the second path are superposed by a biprism, and its intensity distribution is measured. Coherence is measured from a relation between a spin direction rotation angle, a delay time, and a visibility of an interference fringe.