A method and apparatus for analyzing vapors generated from explosives in which vapors containing nitrogen monoxide and/or nitrogen dioxide are generated by decomposing explosives by increasing the temperature of the explosives, primary ions and neutral molecules are generated from air. The generated primary ions and the nitrogen monoxide and/or nitrogen dioxide contained in the generated vapors are allowed to react with each other in an area inhibited or prevented from being penetrated by the generated neutral molecules, and the nitrogen monoxide and/or nitrogen dioxide contained in the generated vapors is ionized. The ionized nitrogen monoxide and/or nitrogen dioxide is subjected to mass spectrometry, and an amount of the nitrogen monoxide and/or nitrogen dioxide contained in the generated vapors by decomposing the explosives is determined.