PURPOSE: To shorten a processing time by providing a discriminating means for discriminating a data which is an object of a garbage collection, among data stored in a main storage device, on a data processing device used for an Lisp processing.

CONSTITUTION: As an Lisp processing advances, a data for constituting a reflexive routine is stored ina stack 1 in a state that a code "0" is put to an address of a data which is an object of a garbage collection, and a code "1" is put to a frame pointer of a return address, high-order frame being a data which cannot become the object, and the number of an argument, at every one word. A discriminating circuit 5 outputs a read inhibiting signal to a read controlling circuit 6, when a identification code is "1". The read controlling circuit 6 executes a processing, in case when the discriminating circuit 5 does not output the read inhibiting signal. In such a way, the processing time required for a garbege collection can be shortened.