Measurement apparatus

A measurement apparatus comprising:

• an optical resonator that resonates light;
• a light source that generates light for irradiation of the optical resonator;
• and
• a photodetector that detects light taken out of the optical resonator, wherein
• the optical resonator includes
• a plurality of mirrors,
• a holder that holds the plurality of mirrors,
• a first tubular portion including opposing ends in contact with the holder, the first tubular portion defining a space where the plurality of mirrors are accommodated,
• a second tubular portion provided inside of the first tubular portion along the first tubular portion, and
• a temperature adjustment portion that adjusts a temperature in the inside of the first tubular portion,
• the holder is composed of a material lower in thermal expansion coefficient than the first tubular portion,
• the first tubular portion includes
• a first portion composed of a material higher in thermal conductivity than the holder, and
• a second portion higher in elasticity than the first portion, and
• the second tubular portion is composed of a material equal to or higher than the first portion in thermal conductivity and provided as far as positions of the plurality of mirrors on an inner side of the second portion.