A time synchronization system comprises a time master, a time slave, and a management node which are coupled to one another via a plurality of networks. The time master transmits to the time slave a time packet at a given timing through at least one of the plurality of networks. The time slave has a time correcting part for receiving the time packet transmitted from the time master and for correcting time based on the received time packet. The management node has: a network switching determining part for determining whether to switch the network for transmitting a time packet to another of the plurality of networks; and a network switching notifying part for notifying, in a case where it is determined that the network for transmitting the time packet is to be switched, information for identifying the switched-to network to the time slave.