A communication conditions determination method, a communication conditions determination system, and a determination apparatus are provided in which the conditions of communication which is performed through a plurality of communication networks are determined without setting up a special apparatus on all the communication networks and without increasing the existing traffic. In a first communication network 100 and a second communication network 200 which are connected by a first connection apparatus 1 such as a router, a determination is made as to whether the source of a packet passed through the second communication network 200 is the first connection apparatus 1 or an apparatus other than the first connection apparatus 1. Packets whose respective sources are the first connection apparatus 1 and packets whose respective sources are an apparatus other than the first connection apparatus 1 are individually summarized. By comparing summarized results, the communication conditions are determined.