A spray drying system for drying wastewater to be dried, the spray drying system comprising: an exhaust gas introduction line for introducing the exhaust gas discharged from an exhaust gas generation source, the exhaust gas introduction line being connected to a plurality of exhaust gas ducts (72,72a,72b) for allowing the exhaust gas to flow through, the plurality of exhaust gas ducts (72,72a,72b) being formed by branching into a plurality of gas ducts at a system branch part, from a single upstream flue gas duct that guides the exhaust gas generated in the exhaust gas generation source to outside, wherein the plurality of exhaust gas ducts (72,72a,72b) merge into a single flue gas duct at a system merge part disposed downstream of the system branch part, the exhaust gas introduction line connected to each of the plurality of exhaust gas ducts (72,72a,72b) downstream of the system branch part and upstream of the system merge part and configured to extract the exhaust gas from each of the plurality of exhaust gas ducts (72,72a,72b); and at least one spray drying device connected to the exhaust gas introduction line and configured to bring the exhaust gas introduced from the exhaust gas introduction line into contact with the wastewater, wherein the number of the at least one spray drying device is smaller than the number of the plurality of exhaust gas ducts (72,72a,72b), and wherein the exhaust gas introduction line includes: a plurality of upstream-side exhaust gas introduction lines (21,21a-c) connected to the respective exhaust gas ducts (72,72a,72b); an introduction-side merge part at which each of the upstream-side exhaust gas introduction lines merge; and a single downstream-side exhaust gas introduction line connecting the introduction-side merge part and the at least one spray drying device; wherein the spray drying system further comprises: a first flow-rate adjusting part disposed in the downstream-side exhaust gas introduction line; and a second flow-rate adjusting part disposed in each of the plurality of upstream-side exhaust gas introduction lines (21,21a-c); an exhaust gas discharge line connecting the spray drying device and the plurality of exhaust gas ducts (72,72a,72b); a temperature detection unit disposed in a bottom part of the spray drying device or the exhaust gas discharge line; and a control device configured to control the first flow-rate adjusting part so that a temperature detected by the temperature detection unit is not lower than an evaporation temperature (T 0) of the wastewater. an exhaust gas introduction line for introducing the exhaust gas discharged from an exhaust gas generation source, the exhaust gas introduction line being connected to a plurality of exhaust gas ducts (72,72a,72b) for allowing the exhaust gas to flow through, the plurality of exhaust gas ducts (72,72a,72b) being formed by branching into a plurality of gas ducts at a system branch part, from a single upstream flue gas duct that guides the exhaust gas generated in the exhaust gas generation source to outside, wherein the plurality of exhaust gas ducts (72,72a,72b) merge into a single flue gas duct at a system merge part disposed downstream of the system branch part, the exhaust gas introduction line connected to each of the plurality of exhaust gas ducts (72,72a,72b) downstream of the system branch part and upstream of the system merge part and configured to extract the exhaust gas from each of the plurality of exhaust gas ducts (72,72a,72b); and at least one spray drying device connected to the exhaust gas introduction line and configured to bring the exhaust gas introduced from the exhaust gas introduction line into contact with the wastewater, wherein the number of the at least one spray drying device is smaller than the number of the plurality of exhaust gas ducts (72,72a,72b), and wherein the exhaust gas introduction line includes: a plurality of upstream-side exhaust gas introduction lines (21,21a-c) connected to the respective exhaust gas ducts (72,72a,72b); an introduction-side merge part at which each of the upstream-side exhaust gas introduction lines merge; and a single downstream-side exhaust gas introduction line connecting the introduction-side merge part and the at least one spray drying device; a plurality of upstream-side exhaust gas introduction lines (21,21a-c) connected to the respective exhaust gas ducts (72,72a,72b); an introduction-side merge part at which each of the upstream-side exhaust gas introduction lines merge; and a single downstream-side exhaust gas introduction line connecting the introduction-side merge part and the at least one spray drying device; a first flow-rate adjusting part disposed in the downstream-side exhaust gas introduction line; and a second flow-rate adjusting part disposed in each of the plurality of upstream-side exhaust gas introduction lines (21,21a-c); an exhaust gas discharge line connecting the spray drying device and the plurality of exhaust gas ducts (72,72a,72b); a temperature detection unit disposed in a bottom part of the spray drying device or the exhaust gas discharge line; and a control device configured to control the first flow-rate adjusting part so that a temperature detected by the temperature detection unit is not lower than an evaporation temperature (T 0) of the wastewater.