Abstract: Windows 2 which allow infrared light to be transmitted therethrough are opened at opposed positions of side walls of a flow tube 1, respectively. A hexagonal frame 6 is air tightly attached to each of the apertures. Each frame 6 is protruded from the inner face of the flow tube 1. A transparent window on which an anti-fogging layer 5 is formed stretches on the inner face of each of the frame 6, so that waterdrops flowing through the flow tube 1 are caused to flow along both the sides of the frame 6, thereby preventing the waterdrops from flowing over the anti-fogging layer 5.

Abstract: A capnometer includes an airway adaptor for introducing a respiratory gas into the analyzer, an infrared radiation source emitting infrared radiation passed through the airway adaptor, a beam splitter for reflecting and transmitting infrared radiation that impinges on the beam splitter, first detecting means for detecting the infrared radiation reflected by said beam splitter and transmitting through said beam splitter, second detecting means for detecting the infrared radiation reflected by said beam splitter and transmitting through said beam splitter; a gas cell filled with CO2 gas, said gas cell being located between one of said first and second detecting means and said beam splitter and processing means for processing a concentration of carbon dioxide gas by using output signals of said first and second detecting means.