It takes a processing time to perform a security process on a time synchronization message, thus the difference of a delay time required for the security process can be made between a time at which the time synchronization message is actually transmitted and a transmission time assigned to the time synchronization message, and therefore, the difference between the actual transmission time of the time synchronization message and the assigned transmission time needs to be reduced. In generation of a secure time synchronization message in the synchronization system according to embodiments of the present invention, most of the security processes is performed in an upper layer which is an MAC layer or a higher layer, and processes including the assignment of the transmission time and assignment of authentication information for authenticating validity of the transmission time are performed in a physical layer.