Disclosed is an apparatus for generating a ranging pseudo noise code used for a terminal of a portable internet system of an OFDM access scheme. The apparatus for generating ranging pseudo noise code detects a cell ID number using a preamble signal transmitted from a base station covering the terminal, detects a ranging pseudo noise code mask value using the detected cell ID number and system parameters input from the base station, and generates a ranging pseudo noise code using the detected cell ID number and the ranging pseudo noise code mask value. With the above structure, a constant initial value can be used irregardless of the cell ID number of the base station, and a desired ranging pseudo noise code can be generated as fast as possible so as to have a desired offset.