To correct the drift of the mass number of ions, due to by the heating of the ceramic holder of a quadrupole without using a temperature sensor.

The relation between the electric power fed to a quadrupole 40 and the temperature of a holder 45 is measured, in advance prior to the measurement of an unknown sample, constants R, C are obtained in approximation to the input/output of the primary RC low pass filter circuit, and they are stored in a memory 31. A CPU 30 integrates the voltage value data which are the target value of the applied voltage for each unit time, at the time of the actual sample measurement. The holder temperature is calculated by the approximate expression containing the constants R, C, and the voltage value data corrected with the voltage correction quantity corresponding to the temperature are inputted to a D/A converter 32. The voltage applied to rod electrodes 41-44 is corrected, and the drift of the mass number is resolved.