Mass Spectrometer and Method of Using the Same

A mass spectrometer is provided which is mounted on a wall portion of a chamber and analyzes a gas to be analyzed existing in the chamber. The mass spectrometer includes: a measurement unit which is inserted into the chamber at the time of mounting the mass spectrometer to the chamber and measures each partial pressure of gaseous components in the gas to be analyzed with respect to mass-to-charge ratios; a control unit which is disposed outside of the wall portion at the time of mounting the mass spectrometer on the chamber and is used to manipulate the measurement unit; and a display unit which is disposed outside of the wall portion at the time of mounting the mass spectrometer on the chamber and displays the measurement result of the measurement unit. Here, the measurement unit, the control unit, and the display unit are disposed close to each other.