Four rod electrodes (50a to 50d) for separating ions according to a mass-to-charge ratio are held by a rod holder (51). The rod holder (51) is placed on a metal holder sustaining stand (52) provided on a bottom surface of a vacuum housing (1), and is fixed while being pressed by a fixation band (53) fixed to the holder sustaining stand (52) with screws (56). The fixation band (53) is made from phosphor bronze having higher thermal conductivity than thermal conductivity of stainless steel or the like. Therefore, heat generated in the rod holder (51) due to dielectric loss is not only directly transmitted to the holder sustaining stand (52), but also efficiently transmitted to the holder sustaining stand (52) through the fixation band (53). With this, the heat of the rod holder (51) is efficiently dissipated, and non-uniformity of temperature of the rod holder can be reduced.