When time synchronization between communication apparatuses is performed with PTP, a PTP packet storing a time stamp is transmitted/received. At that time, an RTC is provided in a PTP packet generation unit within the communication apparatus. An RTC is also provided in a PTP packet transmission unit. These RTCs are time-synchronized by a hardware operation based on PPS/System CLK. The RTCs of the PTP packet generation unit and the PTP packet transmission unit are time-synchronized, whereby a highly precise time stamp and correction value for a time can be obtained.