Ion detector and mass spectrometer

A mass spectrometer comprising:

• an ionization unit;
• a mass separation unit;
• and
• an ion detector, wherein
• the ion detector includes
• a conversion dynode including a conversion region where electrons are emitted by incident ions,
• an electron multiplier including a first-stage dynode on which the electrons are incident,
• a box electrode housing the conversion dynode, and including a first opening through which the ions traveling to the conversion region pass and a second opening through which the electrons traveling to the first-stage dynode from the conversion region pass,
• a conductive shielding portion disposed in the first opening and including a gap through which the ions traveling to the conversion region pass, and
• a potential application unit which applies a first potential to the conversion dynode, applies a second potential to the first-stage dynode, applies a third potential to the box electrode, and applies a fourth potential to the shielding portion,
• the first potential and the third potential have polarities opposite to a polarity of the ions,
• the second potential is higher than the first potential, and
• the third potential and the fourth potential are substantially the same potential.