A method for analyzing communication qualities between virtual machines serving as transmission sources and virtual machines serving as transmission destinations on a virtual network includes identifying, by a computer, based on the temporal sequence of the input queue information and the temporal sequence of the output queue information, a first pair and a second pair as mirroring targets, wherein the input queue information indicates a first queue length indicating a number of pieces of data addressed from one of the transmission sources to one of the transmission destinations, wherein the output queue information indicates a second queue length indicating a number of pieces of data included in an output queue of the one of the transmission destinations.