PURPOSE: To make highly reliable ion implantation possible by positioning a base board at any required angle by arranging a reference position setting means thereby enhancing the setting accuracy of the base board.

CONSTITUTION: A rotary shaft 10 provided with a base board holder 4 for holding a base board 2 is rotated with a rotating of a motor 30 transmitted with a rotation transmission mechanism 18. In that case, a reference position setting means or a detecting piece 36 and a photosensor 38 provided at the rotary section of the rotation transmission mechanism 18 sets a reference position. The rotary shaft 10 is rotated by any required angle from the reference position to position-set the base board 4. This enables to set the position of the base board 4 based on an angle setting input and to realize ion implantation of high accuracy and high reliability.