A dual band slot antenna for an electronic device includes an antenna body with elongated first and second slots defined therein and a coaxial feeder cable having a conductive inner core wire and a conductive outer shield. The longitudinal slot may have a width that is wider than the outer diameter of the widest of the tubular portions, but narrower than the width of the narrowest of the flanges. The retractor includes a plurality of flexible arms and a plurality of rigid arms as well as a surgery target immobilizing element. The reference variable corresponding to the angular position of the master axis is determined, slave axis displacement data corresponding to the reference variable is read out, and the slave axis is positioned in accordance with the position of the master axis on the basis of this displacement data.