A mass spectrometer (1) is provided with: an ionization chamber (10) for ionizing a sample (S) on its surface at an analysis point through irradiation by a laser beam; an analysis chamber (23) having a mass spectroscope (24) for detecting ions; a middle vacuum chamber (21, 22) arranged between the ionization chamber (10) and the analysis chamber (23); and an introduction pipe (12) or an introduction hole for allowing the inside of the housing (11) of the ionization chamber (10) to communicate with the inside of the middle vacuum chamber (21), wherein ions and fine particles, which have not been drawn into the introduction pipe (12) or introduction hole, can be prevented from spreading inside of the chamber. The structure of the mass spectrometer (1) further includes: an exhaust pipe (13); and a fan (15) for drawing air into the exhaust pipe (13) so that air that contains ions and/or fine particles, which have not been introduced into the introduction pipe (12) or introduction hole, can be suctioned up into the exhaust pipe (13) when the fan (15) is in operation.