Tunable interference filter

A tunable interference filter comprising:

• a first substrate provided with a first reflection film;
• and
• a second substrate provided with a second reflection film facing the first reflection film with a gap between the first reflection film and the second reflection film, wherein
• the first substrate includes
• a movable portion that is a portion where the first reflection film is provided,
• a diaphragm portion surrounding the movable portion, and
• a base portion supporting the movable portion via the diaphragm portion to allow displacement of the movable portion in a thickness direction of the first substrate,
• the diaphragm portion is a portion in which a thickness at the first substrate is thinner than a thickness of the base portion due to a groove opened in a surface of the first substrate, and
• the width of a bottom portion of the groove is larger than a width of an opening of the groove in a width direction of the groove.