A mass-spectrometry apparatus includes a substrate for mass spectrometry used in surface-assisted laser desorption/ionization mass spectrometry, a light irradiation means that irradiates sample S in contact with a surface of the substrate with measurement light L1 to desorb analyte R in sample S from the surface, a metal probe that generates near-field light at the leading end thereof by irradiation with measurement light L1, a detector that detects desorbed analyte Ri, and an analysis means that performs mass spectrometry on analyte R based on a detection result by the detector. The leading end of the metal probe is arranged in such a manner that the near-field light generated by irradiation with measurement light L1 is in contact with a measurement light irradiation portion of sample S. The metal probe is arranged, with respect to the measurement light irradiation portion, at a position different from the direction of the detector.