A tandem time-of-flight mass spectrometer is offered which can perform MS/MS measurements efficiently without sample wastage by ingeniously combining flight time ranges required by precursor ions with measurement times actually taken to measure the precursor ions. The mass spectrometer has an array input means for causing the flight time ranges required by selected precursor ions and the actually taken measurement times in which the precursor ions are measured to be appropriately arrayed in a time-sequential manner such that the flight time ranges and measurement times do not overlap each other.