Method for mass spectrometry and mass spectrometer

A mass spectrometer comprising:

• a cooling section configured to perform cooling of ions to be analyzed, by making the ions come in contact with a cooling gas;
• an ion-accelerating section configured to impart kinetic energy to the ions after the cooling;
• a time-of-flight mass-separating section including a flight space for separating ions according to mass-to-charge ratios of the ions, the flight space configured so that the ions having kinetic energy imparted in the ion-accelerating section are introduced into the flight space;
• a detecting section configured to detect the ions separated by the time-of-flight mass-separating section;
• and
• a gas-supply regulating section configured to regulate an amount of supply of the cooling gas to the cooling section so that the amount of supply is changed according to a known or estimated number of charges of an ion to be analyzed.