PURPOSE: To make it possible to suppress birefringence and to enhance productivity, by incorporating a specified phosphorous acid ester into a polycarbonate resin, and continuously extruding the resultant resin.

CONSTITUTION: A bis(hydroxyphenyl)alkane polycarbonate resin containing 0.005 to 0.5wt.% of a phosphorous acid ester of the formula and having a number average molecular weight of 18000 to 50000 is extruded to continuously produce a base. In the formula, each of R1 and R2 is an alkyl or aryl, and R3 is hydrogen, an alkyl or aryl. A Polycarbonate resin sheet extruded through a T-die 4 of an extruder 5 is pressed, in a softened state, by a rugged stamper surface of a forming roller 2 and a specular surface of a pressure roller 3, whereby signals representing the rugged stamper form are transferred successively to the surface of the resin base 1. The resin temperature is preferably 200 to 400°C, and the temperature of the forming roller 100 to 200°C. A base for an optical recording medium having excellent transparency and a low birefringence can be produced continuously with favorable productivity.