An apparatus and a method for manufacturing an optical fiber preform by modified chemical vapor deposition (MDVD). The apparatus includes a heating device for heating a rotating substrate tube while moving in a predetermined direction, wherein the heating unit has a first heating unit located at the front with respect to the moving direction, for heating the substrate tube with a relatively low flame pressure, and a second heating unit located at the rear of the first heating means with respect to the moving direction, for heating the substrate tube with a relatively high flame pressure. The first and second heating units are selectively used for deposition and collapsing, such that the duration and temperature of collapsing can be reduced.