A wafer holder for holding a wafer includes a wafer holder base, a wafer fixing part, holder pins, a bearing, a housing, and a coil spring. The wafer fixing part is fixed to an outer circumference of a wafer holder. The holder pins are arranged to face the wafer fixing part. The holder pin is rotatably supported by the bearing. The holder pins are movably supported along the diameter direction of the wafer holder base by the coil spring. In the process of holding a side of the wafer with the holder pins, when force from the wafer works on the holder pins, the holder pins are rotated with a Z axis as a center, thus reducing frictional force between the holder pin and the wafer. Accordingly, it is possible to prevent particle generation from holding an implanting object.