A wafer holding assembly is provided that is capable of preventing the temperature difference generated between a wafer and a holding pin through beam irradiation.In one embodiment, the wafer holding assembly has a plurality of holding pins for holding a wafer in the ion implanting apparatus, the holding pin comprises a head contacting with an end face of the wafer to control motion of the wafer and a flange projecting from the head to place the wafer, and the head is provided with a canopy portion extending in a direction different from a side placing the wafer.