An ion beam etching device includes a grid provided between a treatment chamber and a plasma generation chamber, and for forming an ion beam by drawing ions from the plasma generation chamber; a gas introduction unit for introducing discharge gas into the plasma generation chamber; an exhaust for exhausting the treatment chamber; a substrate holder; a control unit to receive a measurement result of an in-plane film thickness distribution before the substrate is processed; and an electromagnetic coil provided outside of the plasma generation chamber in a ceiling portion opposite to the grid of the plasma generation chamber. The electromagnetic coil includes an outer coil provided on an outer circumference of the ceiling portion and an inner coil provided on an inner circumference of the ceiling portion, and the control unit controls the currents applied to the outer coil and the inner coil in accordance with the measurement result.