An evaporator chamber for mixing water vapor with respiratory gas has a supply opening for the respiratory gas, an inlet opening for the water vapor and an outlet opening for the humidified respiratory gas. With the evaporator chamber, an excellent mixing is achieved with the smallest possible structural volume. The evaporator chamber is configured as a hollow body (1) having an essentially circularly-shaped inner wall surface (5). The supply opening (4) on the upper end of the hollow body (1) is arranged in a manner which conducts in the respiratory gas essentially tangentially to the inner wall surface (5). The outlet opening (6) is located at the lower end of the hollow body (1) and the inlet opening (9) lies between the supply opening (4) and the outlet opening (6).