To provide a heat amount monitoring device for continuously and accurately measuring and monitoring heat output amount taken away by exhaust gas discharged from a furnace body, in an arc melting facility.

In the heat amount monitoring device in the arc melting facility provided with an arc furnace main body 1, a combustion chamber 11 for burning unburned components in the discharged exhaust gas, a cooling chamber 13 for cooling the exhaust gas discharged from the combustion chamber, heat amount held in the exhaust gas after cooled down is calculated from temperature 28 and flow rate 29 of the exhaust gas after the unburned components in the exhaust gas are completely burned and cooled down and ambient atmospheric temperature 27 of the arc furnace main body. Calculated heat of the exhaust gas is added to measured value of heat extracting amount to cooling water from the exhaust gas between a discharging point of the exhaust gas of the arc furnace main body and measuring points of temperature and flow rate of the exhaust gas, and the added value is determined as heat amount taken away by the exhaust gas at the discharging point of the arc furnace main body and heat output amount from the arc furnace main body by the exhaust gas is monitored based on this heat amount.