A tunable filter including; a fixed substrate provided with a fixed reflecting film and capable of transmitting light having a shorter wavelength than infrared light; a movable substrate provided with a movable section equipped with a movable reflecting film and disposed to the fixed substrate so that the movable reflecting film and the fixed reflecting film faces each other with a predetermined length of gap; and a drive section for varying the length of the gap by displacing the movable section with respect to the fixed substrate, wherein light entering the gap from the outside is repeatedly reflected by the movable reflecting film and the fixed reflecting film for outputting light having a wavelength corresponding to the length of the gap, and the movable section is provided, at an area to which the movable reflecting film is disposed, with a light transmitting section capable of transmitting light having a shorter wavelength than infrared light and for inputting/outputting light from/to the outside.