Mass spectrometer having lens unit supported with springs

A mass spectrometer comprising:

• a lens unit for generating an ion beam by converging and accelerating ions obtained by ionizing a sample;
• a main body which contains said lens unit in an airtight manner, said main body including an ionization part, a beam converging part and a detection part, said ionization part containing means for generating ions of a sample, said beam converging part containing said lens unit, said detection part containing means for detecting ions received from said beam converging part, said main body further including a first partition wall between and separating said ionization part and said beam converging part and a second partition wall between and separating said beam converging part and said detection part, said main body having an opening in said beam converging part for passing said lens unit to pass therethrough and a cover for closing said opening;
• a lens-unit holder to which said lens unit is affixed;
• a base plate with a hole for passing ions therethrough to said lens unit;
• forward-biased springs;
• backward-biased springs;
• and
• spring holders affixed to said main body for deforming said forward-biased springs to cause said base plate to be elastically pressed against said first partition wall and said backward-biased springs to cause said lens-unit holder to be pressed against said second partition wall to thereby position said lens unit and said base plate at specified positions inside said main body.