Patent ID: 7474412

Claim:
An etalon device comprising: a first parallel plate and a second parallel plate arranged to face each other; a first holder portion which holds the first parallel plate, a second holder portion which holds the second parallel plate, and a housing portion arranged outside of the first holder portion and the second holder portion, wherein at least one of the first holder portion and the second holder portion has a concavity with an inside diameter larger than an outside diameter of a mating parallel plate, which is the first parallel plate or the second parallel plate, so that the mating parallel plate rests in the concavity, wherein inside the concavity, a receiving portion, with which the mating parallel plate is in contact, is provided, and wherein at a position where the receiving portion is in contact with the mating parallel plate, an inclined face is formed at least on one of the receiving portion and the mating parallel plate.