Provided is an ion implantation method of transporting ions generated by an ion source to a wafer and implanting the ions into the wafer by irradiating an ion beam on the wafer, including, during the ion implantation into the wafer, using a plurality of detection units which can detect an event having a possibility of discharge and determining a state of the ion beam based on existence of detected event having a possibility of discharge and a degree of influence of the event on the ion beam.