A gas ratio control device for anesthesia apparatus, includes an anesthetic gas feed line, which has, in a series-connected arrangement, a control valve with an inlet chamber, an anesthetic gas-adjusting valve and a first measuring resistance, and an oxygen feed line, which has a second measuring resistance, wherein the dynamic pressure received from the measuring resistances is sent to a proportional element, which controls the control valve. A flow-proportional addition of the anesthetic gas is possible even at low oxygen flow rates. This is achieved by the outlet chamber and the first pressure chamber being connected to one another in one piece in terms of flow. The anesthetic gas-adjusting valve is arranged in front of the inlet chamber of the control valve in terms of flow. A flow resistance is provided between two chambers limited by diaphragms of the proportional element.