Abstract: Disclosed is a pattern forming apparatus using a quadrupole lens system to control the cross section of a beam of electrons or ions to be projected onto a plate-like object. A variety of rectangular beams can be formed by electrically controlling the quadrupole lens system, and thus a desired pattern can be produced in the form of combination of rectangle and line pattern elements when the plate-like object is exposed to the beam of electric charged particles. The pattern forming apparatus according to this invention is useful particularly in fabricating integrated circuits, semiconductor devices and other precision devices.