A network analysis assistance device for assisting analysis of networks in a system comprising a first device, a gateway device and a second device, the network analysis assistance device comprising: first electronic message collection means connecting to a first network to which the first device and the gateway device are connected, and collecting electronic messages traveling on the first network; second electronic message collection means connecting to a second network to which the gateway device and the second device are connected, and collecting electronic messages traveling on the second network; a mapping table in which the correlation between an electronic message travelling from the first network to the gateway device and an electronic message travelling on the second network from the gateway device, and the correlation between an electronic message travelling from the second network to the gateway device and an electronic message travelling on the first network from the gateway device, are defined; electronic message association means associating electronic messages collected by the first electronic message collection means and electronic messages collected by the second electronic message collection means, with reference to the mapping table; and status analysis means determining, based on delay times, whether or not receipt of electronic messages between the first network and the second network is accomplished normally, each of the delay times found by subtracting an acquisition time of an electronic message input into the gateway device from an acquisition time of an electronic message output from the gateway device, the input electronic message associated with the output electronic message by the electronic message association means. first electronic message collection means connecting to a first network to which the first device and the gateway device are connected, and collecting electronic messages traveling on the first network; second electronic message collection means connecting to a second network to which the gateway device and the second device are connected, and collecting electronic messages traveling on the second network; a mapping table in which the correlation between an electronic message travelling from the first network to the gateway device and an electronic message travelling on the second network from the gateway device, and the correlation between an electronic message travelling from the second network to the gateway device and an electronic message travelling on the first network from the gateway device, are defined; electronic message association means associating electronic messages collected by the first electronic message collection means and electronic messages collected by the second electronic message collection means, with reference to the mapping table; and status analysis means determining, based on delay times, whether or not receipt of electronic messages between the first network and the second network is accomplished normally, each of the delay times found by subtracting an acquisition time of an electronic message input into the gateway device from an acquisition time of an electronic message output from the gateway device, the input electronic message associated with the output electronic message by the electronic message association means.