A gate electrode (10A) used as a shutter gate includes a pair of conductive fixture members (131, 132) made of metal and identical in size attached to the inside of a rectangular opening (12) of a ceramic base (11), along with insulating fixture members (141, 142) made of ceramic attached to the inner sides of the conductive fixture members. Two comb electrodes (151, 152) as one pair have connecting portions (151a, 152a) adhered to the conductive fixture members (131, 132) as well as thin-wire electrodes whose distal ends are adhered to the insulating fixture members (141, 142). By setting length L of the opening (12) and width D of the conductive fixture members (131, 132) to appropriate values according to the coefficient of thermal expansion of each of those members, the elongation of the electrodes which accompanies an increase in temperature can be balanced by the increase in the distance between the adhered positions of the electrodes to prevent the electrodes from being excessively taut or slack. Therefore, the drift region can be heated to a higher temperature than conventional levels to perform a high-accuracy, high-resolution analysis free from the influence of residual water vapor or similar particles.