A hollow core fiber was utilized as a capillary flow-cell for the infrared spectroscopy in gas phase that has the 1 m optical length and requires the sample volume of 2 ml. The system was applied to the qualitative analysis of hydrochloric acid. As a result, the specific spectrum of hydrochloric gas was successfully obtained at 10 times higher absorbance compared with an ordinary gas cell with 10 cm optical length. The capillary flow cell system developed in the present study can be a powerful tool in forensic chemistry for the analysis of hydrochloric acid and other volatile toxic substances.