Fringelike electron emission patterns emitted from Pt field emitters fabricated by focused-ion-beam-induced deposition (FIBID) were investigated by field-emission microscopy and in situ field-ion microscopy (FIM). The FIM image with electron emission sites showed adjacent two emission sites within a diameter of a Pt nanocrystal. These results indicate that the origin of fringelike electron emission patterns of Pt field emitters fabricated by FIBID are the electron wave interference induced by electrons emitted from adjacent two electron emission sites within a Pt nanocrystal.