PURPOSE: To prevent the coagulation of an additive component for diffusion and collection in the side end section of the opening section of a tube body, and to obviate the deterioration of the quality of a silicon wafer due to evaporation at the time of the extraction of a boat by forming the discharge opening of the tube body projected to the outside of a heater in the lowermost surface of the tube body.

CONSTITUTION: The introducing port 5 and discharge opening 27 of an additive component for a diffusion are formed to a tube body 3 inserved into a heater 2 and projected to the outside of the heater 2, and the discharge opening 27 is shaped to the lowermost surface of the tube body 3. Consequently, even when the additive component for the diffusion is coagulated, the additive component is discharged quickly from the discharge opening 27 without being collected. When a lower-side inner wall in the tube body 3 is tilted in the direction that the discharge opening 27 is formed, the additive component for the diffusion collected over a wide range in the rube body 3, particularly in the longitudinal direction is discharged easily. Accordingly, the coagulation of the additive component for the diffusion and collection of same in the side end section of the opening section of the tube body 3 are prevented without making a temperature in the tube body 3 unstable, thus obviating the deterioration of the quality of a silicon wafer.