A pin removal structure used in printed circuit board drilling machine comprised of a main body, a first driving member, a first driving rod, a collet member, a lower mounting cover, a socket, a second driving member, a plurality of second driving rods, and an air pressure control valve member. A control unit 5 controls the hydrogen draw pump 12 such that hydrogen drawing power is increased to a level larger than that required for normal operation and controls the hydrogen control valve 11 such that opening degree is decreased. The mucositis is preferably caused by radiotherapy andor chemotherapy and preferably refers to oral mucositis.