To provide an ion implanting device provided with an ion source head having a structure capable of preventing any circulation of gas not contributive to ionization and adhesion of the gas to members disposed therearound and of stabilizing a high electric field at an ion source generating portion.

An ion implanting device is provided at the head thereof with an arc chamber 7 and a first gas introducing pipe 18 and second gas introducing pipes 20 (hereinafter referred to as 'a gas introducing pipe') disposed near a surface opposite to a surface having an ion source emitting port 8 of the arc chamber 7; and at the bottom thereof with a support plate 9 including an ion source head 5 supported via a source mounting flange with application of a high voltage and an insulating bushing for insulating the high voltage and fixing the source mounting flange to an outer casing in a vacuum chamber. The outer diameter of a gas shield plate 21 shielding the surroundings of the inlets of the gas introducing pipes is set in such a manner as to be greater than a maximum value of the outer diameter of the arc chamber 7 and be smaller than the inner diameter of the insulating bushing.