An optical device includes a telecentric optical system, a variable wavelength interference filter, and a detection section, the variable wavelength interference filter includes a first reflecting film, a second reflecting film provided to a movable section, and an electrostatic actuator adapted to displace the movable section, an effective measurement area capable of transmitting a light with a wavelength, which is within a predetermined allowable range centered on a measurement center wavelength when an amount of the displacement of the movable section takes a maximum displacement value, is set in the first reflecting film and the second reflecting film, and the telecentric optical system guides the incident light to the variable wavelength interference filter so that a principal ray of the incident light is parallel thereto and perpendicular to the first reflecting film, and at the same time, collects the incident light in the effective measurement area.