A mass spectrometer including a sprayer for spraying a sample solution, a needle electrode for ionizing the sample contained in the sample solution, an aperture for introducing the ions of the sample into a lower pressure region having a pressure lower than the pressure of a region in which the needle electrode is disposed, and a mass spectrometric apparatus for analyzing the ions introduced from the aperture. A direction of a spray caused by the sprayer is almost perpendicular to or at an angle with respect to a center axis of the aperture, and a tip of the needle is disposed facing to an electrode having the aperture.