<p>A secondary ionization zone (33) where secondary ionization is conducted by laser irradiation is disposed at the outlet of a heating capillary (7) through which ions discharged from an ionization chamber (1) where MALDI ionization is conducted in an atmospheric-pressure atmosphere are introduced into a subsequent first intermediate vacuum chamber (10). Neutral molecules derived from a sample which have not been ionized in the ionization chamber (1) or have been generated through recombining on the way are carried by a gas flow together with ions and discharged into the first intermediate vacuum chamber (10). However, the laser irradiation ionizes the neutral molecules at a high efficiency at a gas pressure lower than atmospheric pressure. Thus, a larger amount of ions can be sent to a later-stage analysis chamber having a high-vacuum atmosphere than in conventional apparatuses, whereby mass spectrometry can be improved in sensitivity and precision.</p>
