To provide an analyzing device that can determine minor organic substance in the atmosphere rapidly by site extraction while being compact, lightweight and easy to carry by providing a device for selectively eliminating moisture and carbon dioxide gas, at a path for leading sample air into a long optical path gas cell.

An analyzing device body 1 stored in a portable case is provided with a moisture and carbon dioxide gas eliminating column 3, a long optical path gas cell 4 and a suction pump 5 that are connected by a pipeline having sampling cocks 6, 7. As an infrared spectrophotometer system of the body 1, a light source and interferometer module 8, a mirror 9 for making infrared rays enter the cell 4, a mirror 10 for multiple-reflecting the infrared rays in the cell 4, and an MCT detector 11 for detecting the infrared rays are provided. The cock 7 is first opened to actuate the pump 5, and then the cock 6 is opened to lead sample air into the cell 4 through the column 3 to perform determination. It is desirable to fill synthetic zeolite in the column 3.