PURPOSE: To carry out laser ionization neutral particle mass spectrometry efficiently with high sensitivity by scanning both a nonanalytical area and an analytical area, and sputtering the whole sputter area uniformly by combining plural scannings with each other.

CONSTITUTION: A signal to show that a radiating position of an ion beam 2 is within an analytical area is generated from scanning electrode electric power supply 15, and is inputted to a detecting time limiting device 16. Simultaneously with this, a laser beam 9 is generated from a laser generator 8, and prescribed time is delayed from a moment when the signal is inputted, and operation of a pulse counter 14 is started. Time delay is set in the same with necessary time during which a light exciting ion 10 generated just above a sample reaches a detector. When the whole sputter area is sputtered by combining plural scannings with each other, the laser beam is generated only when a beam radiating area is within an analytical area without increasing scanning speed, and photo-ionization of a neutral particle can be carried out efficiently.