A design apparatus generates an optimal design condition by design space exploration. The apparatus including a source code parsing (301) which parses source code and generates a parse tree, a cluster generation task (302) which generates clusters based on the parse tree, each of the clusters including a group of source codes which can operate independently, a log file task (303) which generates a log file based on a structure of the cluster, and a comparison task (304) which compares a first log file of a previous cluster with a second log file of a current cluster and re-uses previous exploration result based on a comparison result, the first log file being obtained from a previous design space exploration, the second log file being generated from a current operation.