Cloud services make use of data center resources so that hosted applications can utilize them as needed. To offer a large amount of computational resources, cloud service providers manage tens of geographically distributed data centers. Since each data center is made up of hundreds of thousands of physical machines, energy consumption is a major concern for cloud service providers. The electric cost imposes significant financial overheads on those companies and pushes up the price for the cloud users. This paper presents an energy-price-driven request dispatcher that forwards client requests to data centers in an electric-cost-saving way. In our technique, mapping nodes, which are used as authoritative DNS servers, forward client requests to data centers in which the electric price is relatively lower. We additionally develop a policy that gradually shifts client requests to electrically cheaper data centers, taking into account application latency requirements and data center loads. Our simulation-based results show that our technique can reduce electric cost by 15 % more than randomly dispatching client requests. We also implemented a prototype of the mapping node, and the experimental results show that its processing time marginally increases compared with that of legacy DNS lookups.