a data processing method for scalability of a parallel computer system includes : obtaining a processing time τ that is the longest processing time in a case where a parallel processing is carried out by p processors and a processing time γ i that is a processing time of parallel calculation portions during an executed processing ; calculating a limit processing time τ lt that is an entire processing time in assuming that the processing time of the parallel calculation portions has become zero , by using the processing time τ and the processing time γ i of the parallel calculation portions ; and outputting a relation between the processing τ and the limit processing time τ lt with respect to the number p of processors to an output device . favorably , the limit processing time τ lt becomes constant without depending on the processing time τ , and it is possible to evaluate the scalability by judging the difference with the favorable state .