an optical divider including at least first and second light-emitting edges that are aligned in a first direction, the optical divider dividing a beam of measured light into at least first and second divided beams of measured light, the optical divider allowing the first and second divided beams of measured light to be emitted in a second direction from the first and second light-emitting edges, respectively;

a first optical element that converts the first and second divided beams of measured light into first and second parallel beans of measured light;

a second optical element that uniaxially condenses the first and second parallel beams of measured light in a third direction, the third direction being perpendicular to the first and second directions;

a photoelectric converter including a plurality of light receiving elements, the plurality of light receiving elements receiving first and second uniaxially condensed beams of measured light from the second optical element, the plurality of light receiving elements being aligned in the first direction so that each of the plurality of light receiving elements receives an equally-divided one of the period of an interference pattern, the interference pattern being caused by an interference between the first and second uniaxially condensed beams of measured light, each of the plurality of light receiving elements generating an electrical signal that depends on an intensity of the equally-divided one of the period of the interference pattern, each of the plurality of light receiving elements having a light-receiving surface that is inclined relative to the third direction; and

a signal processing unit that receives the electrical signals outputted from the plurality of light-receiving elements, the signal processing unit obtaining a wavelength of the measured light from the electrical signals.