A time synchronization system includes at least one time server and a plurality of time clients connected to each other via a network. The time client comprises: a communication unit configured to obtain time information of the time server by transmitting/receiving messages to/from the time server; and a time count control unit configured to synchronize time information of an internal timepiece with time information of the time server. The time count control unit controls transmission of the messages by adjusting transmission intervals of the messages to irregular intervals.