PURPOSE: To enhance the building-up efficiency of ejected glass fine powder in the outer sticking build-up method in the case of producing the optical fiber preform made of quartz-based glass.

CONSTITUTION: Building-up fine powder 12 is ejected from a burner 11 and built up on the surface of the material 13 to be built up. Moreover unbuilt up fine powder 12a is exhausted from an exhaust system. In this method for producing the optical fiber preform, a first exhaust port 15 of this exhaust system is opened in the nearly whole body exclusive of the front face in the burner side of the material 13 to be built up. Further a second exhaust port 16 of the exhaust system is opened in the vicinity of the opposite side (rear side) to the burner of the material to be built up and the ejected flow of the building-up fine powder 12 is straightened. Since the ejected flow of the building-up fine powder 12 is sufficiently infiltrated to the rear side of the material 13 to be built up by the respective exhaust ports 15, 16 especially the second exhaust port 16, the contact area of both the building-up fine powder 12 and the circumferential face of the material 13 to be built up is increased and excellent building-up yield is obtained.