In recent years many public clouds have been available, and not only Infrastructure as a Service (IaaS) but others including Software as a Service (SaaS) as well have been provided by them. We focus on Amazon EC2 and RDSas examples of IaaS and SaaS in a public cloud, respectively, and experimentally compare them in terms of performance and costs in this paper. The results would be helpful for the users in considering which platform they should use for their applications.