A method and an apparatus which continuously separate and measure mercury in an exhaust gas in accordance with each chemical conformation and display a measurement result in real time. According to the method and the apparatus, water-soluble mercury in a gas is absorbed into an absorption solution (7), the gas and the absorption solution (7) are then separated from each other, the water-soluble mercury in the absorption solution (7) is reduced to be converted into gaseous metal mercury and led to an analyzer (20), and metal mercury in the gas which is not absorbed into the absorption solution (7) is led to an analyzer (22) in the form of gas. As a result, the water-soluble mercury and the non-water-soluble mercury contained in the gas can be captured and measured/analyzed in respective measurement systems in accordance with each chemical conformation. In addition, a concentration of the metal mercury and that of the water-soluble mercury in the gas can be continuously monitored in real time. In this analysis, it is preferable to use the absorption solution (7) to absorb an acid gas which is an inhibitive component to mercury measurement, together with the water-soluble mercury.