A communication apparatus (13) according to the present invention is provided with: a storage unit (131) that stored in advance difference information (1311), which is the difference between first time information (t1) and second time information (t2), said first time information (t1) being received from a synchronization source communication apparatus (11) as a time synchronization source connected to a transmission system (12) wherein transmission delay time is different depending on the direction of transmission, and said second time information (t2) obtained from a time synchronization origin (14) other than the transmission system (12); and a time synchronization means (132) that carries out, when the second time information (t2) cannot be obtained from the time synchronization origin (14), time synchronization with the synchronization source communication apparatus (11) using the difference information (1311) read out from the storage unit (131).