In a mass spectrometer utilizing an atmospheric pressure ion source, the amount of un-vaporized droplets that reach a mass spectrometric section is reduced. A mass spectrometer comprises: an ionization section for ionizing a sample at substantially atmospheric pressure; a first and a second intermediate pressure section in which the pressure is maintained lower than the pressure in said ionization section; a high vacuum section in which the pressure is maintained lower than the pressure in said intermediate pressure section and in which a mass spectrometric means for subjecting ions to mass spectrometry is disposed; a first pore electrode disposed between said ionization section and said first intermediate pressure section; an intermediate pore electrode disposed between said first intermediate pressure section and said second intermediate pressure section; and a second pore electrode disposed between said second intermediate pressure section and said high vacuum section. A first converging electrode is provided in the first intermediate pressure section, the first converging electrode having an opening towards the first pore electrode and another opening towards the intermediate pore electrode. The opening towards the first pore electrode has a larger diameter than the opening towards the intermediate pore electrode, such that the first converging electrode has a tapered shape.