A time synchronization method for synchronizing times of a first apparatus and a second apparatus includes transmitting, by the first apparatus, a packet to the second apparatus, the packet including the time of the first apparatus, providing, by a relay apparatus that relays the packet, a value to the packet, the value indicating a reception time upon the reception of the packet, providing, by the relay apparatus, a difference between the value provided to the packet in the providing of reception time and a current time to the packet upon the transmission of the packet, the difference serving as a delay value, and executing, by the second apparatus, a control for time synchronization based on the time of the first apparatus included in the packet and the delay value provided to the packet.