PURPOSE: To reduce an error of the practical ion implanting-amount to a set implanting amount by giving a function to count the neutralize beams by the pressure variation of an implanting member.

CONSTITUTION: The beam current amount and the pressure in an implanting operation by an implanting member 1 is monitored, and the value data is delivered to a beam current correction controller 3. In the controller 3, it is decided whether the beam current is within a set scope or not, the rate of the neutralized beam is decided to calculate the correcting beam current amount, and the result is delivered to a dose controller 2. In the dose controller 2, the practical implanting amount is calculated, and the implantation is carried out until the practical implanting amount reaches to the set implanting amount. Consequently, the error between the set implanting amount and the practical implanting amount can be reduced by correcting the beam component neutralized by the pressure variation of the implanting member 1.