A liquid chromatograph mass spectrometer includes a solvent removing tube, a first ion lens and a second ion lens. Voltages applied to the solvent removing tube, and the first and second ion lenses corresponding to each mass number of a standard sample are studied in advance so that efficiencies of passing ions become best. A voltage scanning pattern is made based on the impressed voltages, and stored in a memory portion. When a scanning measurement is carried out, a control portion controls a current voltage source and a high frequency voltage source according to the voltage scanning pattern, synchronizing with the scanning of the impressed voltage to the quadrupole filter. As a result of the control, an objective ion which is generated by being atomized from a nozzle may effectively pass through the entrance of a quadrupole filter.