A mercury measuring apparatus for measuring mercury contained in a sample composed mainly of hydrocarbon, which apparatus comprises: a column accommodating therein a first adsorbent configured for adsorbing mercury and a reducing agent for reducing monovalent and bivalent mercury into a metal mercury; an injector for injecting the sample into the column; a first heating unit configured for heating the first adsorbent within the column; a second heating unit configured for heating the reducing agent within the column; a mercury collecting tube filled with a second adsorbent configured for adsorbing the metal mercury; a third heating unit configured for heating the mercury collecting tube; a mercury measuring unit configured for measuring by introducing the metal mercury, which is isolated from the mercury collecting tube then heated by the third heating unit, into a sample cell; a gas flow path defining one of an injecting and collecting passage configured for introducing a carrier gas from a gas introducing port so as to flow through the first adsorbent and discharging the carrier gas from a gas discharge port, a reducing and collecting passage configured for introducing the carrier gas from the gas introducing port so as to flow through the first adsorbent, a reducing agent and a second adsorbent and discharging the carrier gas from the gas discharge port, and a measuring passage configured for introducing the carrier gas from the gas introducing port so as to flow through the second adsorbent and a sample cell and discharging the carrier gas from the gas discharge port; a flow path switching valve (V1, V2, V3, V5, V6) configured for selecting one of the gas flow passages (FP1, FP2, FP3, FP4); and a control unit configured for controlling the first heating unit, the second heating unit, the third heating unit, the injector, the flow path switching valve (V1, V2, V3, V4, V5, V6) and the mercury measuring unit. a column accommodating therein a first adsorbent configured for adsorbing mercury and a reducing agent for reducing monovalent and bivalent mercury into a metal mercury; an injector for injecting the sample into the column; a first heating unit configured for heating the first adsorbent within the column; a second heating unit configured for heating the reducing agent within the column; a mercury collecting tube filled with a second adsorbent configured for adsorbing the metal mercury; a third heating unit configured for heating the mercury collecting tube; a mercury measuring unit configured for measuring by introducing the metal mercury, which is isolated from the mercury collecting tube then heated by the third heating unit, into a sample cell; a gas flow path defining one of an injecting and collecting passage configured for introducing a carrier gas from a gas introducing port so as to flow through the first adsorbent and discharging the carrier gas from a gas discharge port, a reducing and collecting passage configured for introducing the carrier gas from the gas introducing port so as to flow through the first adsorbent, a reducing agent and a second adsorbent and discharging the carrier gas from the gas discharge port, and a measuring passage configured for introducing the carrier gas from the gas introducing port so as to flow through the second adsorbent and a sample cell and discharging the carrier gas from the gas discharge port; a flow path switching valve (V1, V2, V3, V5, V6) configured for selecting one of the gas flow passages (FP1, FP2, FP3, FP4); and a control unit configured for controlling the first heating unit, the second heating unit, the third heating unit, the injector, the flow path switching valve (V1, V2, V3, V4, V5, V6) and the mercury measuring unit.