A data center network should provide communication with sufficiently large bandwidth and small delay between all servers. On the other hand, energy consumption of the data center network should be minimized. To satisfy all of the above requirements, in this paper, we introduce the virtual network configured over the data center network constructed of the optical cross connects (OXCs) and the electronic switches. We design the virtual network topology (VNT) so as to achieve sufficiently large bandwidth and small delay with small energy consumption. To calculate the suitable VNT in a short period, we propose the topology called Generalized Flattened Butterfly and a method to set the parameters so as to suit the current condition. In our evaluation, we clarify that our method achieves the sufficient bandwidth and the target maximum number of hops between top-of rack(ToR) switches with small energy consumption.