A supply-liquid producing apparatus (100; 200; 300) comprising: a mixing unit (113; 206; 307) configured to mix a first raw material and a second raw material to produce a mixed liquid; a pump unit (112; 205; 311) configured to change a flow rate of the first raw material to be supplied to the mixing unit (113; 206; 307); a gas-liquid separation tank unit (114; 207; 312) configured to separate the mixed liquid produced by the mixing unit (113; 206; 307) into a supply liquid to be supplied to a use point (119; 213; 318), and exhaust gas to be discharged from an exhaust port (125; 216; 323); a first flow measuring unit (117; 211; 315) configured to measure the flow rate of the supply liquid to be supplied from the gas-liquid separation tank unit (114; 207; 312) to the use point (119; 213; 318); an exhaust valve (124; 215; 322) configured to adjusts an exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323); and an exhaust control unit (127; 218; 324) configured to adjusts the exhaust amount of the exhaust gas to be discharged from the exhaust port (119; 213; 318) by controlling the exhaust valve (124; 215; 322) in response to the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) such that the flow rate of the supply liquid to be supplied to the use point (119; 213; 318) is kept at a constant flow rate, wherein the exhaust control unit (127; 218; 324) is configured to: increase the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) increases with respect to the constant flow rate, and decrease the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) decreases with respect to the constant flow rate. a mixing unit (113; 206; 307) configured to mix a first raw material and a second raw material to produce a mixed liquid; a pump unit (112; 205; 311) configured to change a flow rate of the first raw material to be supplied to the mixing unit (113; 206; 307); a gas-liquid separation tank unit (114; 207; 312) configured to separate the mixed liquid produced by the mixing unit (113; 206; 307) into a supply liquid to be supplied to a use point (119; 213; 318), and exhaust gas to be discharged from an exhaust port (125; 216; 323); a first flow measuring unit (117; 211; 315) configured to measure the flow rate of the supply liquid to be supplied from the gas-liquid separation tank unit (114; 207; 312) to the use point (119; 213; 318); an exhaust valve (124; 215; 322) configured to adjusts an exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323); and an exhaust control unit (127; 218; 324) configured to adjusts the exhaust amount of the exhaust gas to be discharged from the exhaust port (119; 213; 318) by controlling the exhaust valve (124; 215; 322) in response to the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) such that the flow rate of the supply liquid to be supplied to the use point (119; 213; 318) is kept at a constant flow rate, wherein the exhaust control unit (127; 218; 324) is configured to: increase the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) increases with respect to the constant flow rate, and decrease the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) decreases with respect to the constant flow rate. increase the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) increases with respect to the constant flow rate, and decrease the exhaust amount of the exhaust gas to be discharged from the exhaust port (125; 216; 323) in a case where the flow rate of the supply liquid measured by the first flow measuring unit (117; 211; 315) decreases with respect to the constant flow rate.