A communication information detecting device includes: a receiving unit that receives an address resolution request message transmitted from a start-point communication device through L2 broadcast and having an IP address of a target communication device set therein as a target address for L2 address resolution; a generating unit that generates an address resolution request message having the IPv6 address of the target communication device, which is set in the received address resolution request message, set therein as a target address for L2 address resolution; a follow-up processing unit that transmits this address resolution request message through L2 broadcast; a receiving unit that receives an address resolution reply message returned from the target communication device in response to the address resolution request message; and a detecting unit that extracts an L2 address and an IP address concerning the target communication device from the address resolution reply message.