PURPOSE: To reduce the load of a processing system by using a list releasing means when the variables hold a list as a function of the processing system.

CONSTITUTION: Two forms are available to an instruction 6 for the garbage collection GC of software, that is, a form 1 shows 'list-free (argument 1... argument n)' and a form 2 shows 'left side 1 = right side' respectively. The arguments 1 - n of the form 1 mean the variables having pointers to a list and the left and right sides of the form (2) also mean the variables having pointers to the list. A processing system 1 receives the instruction 6 of the form 1 and releases the cells of each list shown in the arguments. Thus the memories consumed by each list are set free so that the GC is carried out. When the instruction 6 of the form 2 is received, the system 1 releases the list held by the variable of the left side and uses the list shown by the variable of the right hand as its own list in order to carry out the GC.