Member for use in mass spectrometer

An insulation spacer to be disposed between a plurality of electrodes arranged along a flight path of ions in a mass spectrometer in which ions accelerated by an electric field are made to fly freely, and are separated and detected with respect to each mass-to-charge ratio depending on a time of flight taken by each ion to reach a detector, the insulation spacer comprising:

• a first portion having a length L1 along the flight path;
• and
• a second portion that is disposed adjacent to the first portion along the flight path, is made of a material different from a material for the first portion, and has a length L2 along the flight path, wherein
• the length L1 and the length L2 are set so as to satisfy L1/α1+L2×α2+L3×α3=0,
• where α1 is a linear expansion coefficient along the flight path of the material for the first portion, α2 is a linear expansion coefficient along the flight path of the material for the second portion, L3 is a length of each of the electrodes along the flight path, and α3 is a linear expansion coefficient of the electrodes along the flight path.