Mass spectrometer

An electrode member having two electrode plain plate portions and one circular portion is created from a single metal plate, where the two electrode plain plate portions belong to every other virtual rod electrode around the ion optical axis and face across the ion optical axis, and the circular portion electrically connects these two electrode plain plate portions. A predetermined number of resin electric holders each holding the electrode member are stacked in the ion optical axis direction, with every other electric member rotated by 90° around the ion optical axis, to form a virtual quadrupole rod type ion guide. Since this configuration reduces the number of components more than ever before and saves a cable for connecting electrode plain plate portions to which the same voltage should be applied, it is possible to reduce the cost and facilitate assembly and regulation in manufacturing and use.