A device unit 46 is constituted by including a lead frame 50 on which a light-emitting mold portion 48 and a light-receiving mold portion 49 are mounted. Moreover, an exterior casing for housing the device unit 46 is constituted of two parts dividable into an upper casing 45 and a lower casing 47. Thus, by holding the device unit 46 by the upper casing 45 and the lower casing 47, external connection terminals 43 constructed of one end portion of the lead frame 50 can be fixed to the exterior casing and positioned in a connector portion 42. Therefore, by reducing the parts count to three and allowing the device unit 46 to be fixed to the exterior casing by a fixed fitting mechanism of the upper casing 45 and the lower casing 47 without performing welding, soldering, thermal caulking or the like, the assembling becomes easy.