Transfer destination of a packet originating from a virtual machine is controlled so as to allow a capture device arranged in a communication network to capture a packet that is transferred using a communication tunnel. A first server acquires a first packet originating from a source virtual machine being operated by the first server, encapsulates the first packet by adding source and destination addresses. The first server further adds a transfer-destination address to the encapsulated first packet to generate a second packet when the first packet is determined to be a target packet to be captured by the capture device. Then, the first server transmits the second packet including the transfer-destination address to the second server using the communication tunnel while the second packet including the first packet is transferred to the transfer-destination address.