To avoid complicated works and perform processing with a good through-put in the ion implanting of the same impurities into different depths.

Impurity gas is introduced to an ion source 2 from an impurity gas source 1 and is ionized. The ion is extracted into a mass spectrograph 4 by an extraction power source 3 connected to the ion source 2. Impurity ion separated by the mass spectrograph 4 is accelerated by a first accelerator 5 up to 10 kV, and partly neutralized by electron emitted from a beam neutralization part 7. When the neutralized impurities and ion are passed through a second accelerator 8, only the ion is accelerated to 120 kV, while the neutralized impurities are not accelerated. The ion accelerated at 150 kV and the impurities accelerated at 30 kV which are not ion go out of the second accelerator 8 and enter into a wafer treatment chamber 11, to be implanted into a wafer W put on a mounting platform 12.