To provide an ion implanter which does not allow a gas to stay in the vicinity of a wafer at ion implantation into the wafer.

The ion implanter comprises a rotating body rotating in a fixed direction, a vacuum chamber for housing the rotating body, and an ion beam ejecting part for irradiating an ion beam to the wafer mounted on the rotating body. The rotating body comprises one or more wafer mounting plates having a wafer mounting surface on one surface, a driving part for rotating the wafer mounting plates, and a gas removing member which is placed/projected on/from the one surface and has a gas removing wall surface on the front side of the rotating direction. Rotation of the wafer mounting plates makes the gas removing wall surface collide with the gas staying on the one surface side of the wafer mounting plates, and removes the gas to the upper side or the back of the wafer mounting surface.