An optical transmission system for performing optical transmission, comprising: an optical switch node including an optical switching processor, the optical switching processor setting substantially identical switching timing for all input ports thereof such that optical signals input from the input ports are substantially switched at identical timing; and a plurality of terminal nodes (20; 20-1 to 20-n) connected to the respective input ports and each including a time difference corrector, the time difference corrector being adapted, during initialization, to transmit a plurality of optical dummy packets to the optical switch node, to then detect synchrony of the optical dummy packets returned thereto after being switched by the optical switch node, and, if synchronization error is detected, to adjust output timing of the optical dummy packets so that timing of arrival of the optical dummy packets at the optical switching processor may coincide with the switching timing of the optical switching processor, to correct a time difference between the switching timing and the arrival timing; characterised in that the time difference corrector is adapted to affix, to each of a head and a tail of the optical dummy packets, position detection information by means of which synchrony of the optical dummy packets is detected, and the time difference corrector is adapted to, if the position detection information detected from the returned dummy packets show synchrony, to judge that the timing of arrival of the optical dummy packets at the optical switching processor is synchronized with the switching timing of the optical switching processor. an optical switch node including an optical switching processor, the optical switching processor setting substantially identical switching timing for all input ports thereof such that optical signals input from the input ports are substantially switched at identical timing; and a plurality of terminal nodes (20; 20-1 to 20-n) connected to the respective input ports and each including a time difference corrector, the time difference corrector being adapted, during initialization, to transmit a plurality of optical dummy packets to the optical switch node, to then detect synchrony of the optical dummy packets returned thereto after being switched by the optical switch node, and, if synchronization error is detected, to adjust output timing of the optical dummy packets so that timing of arrival of the optical dummy packets at the optical switching processor may coincide with the switching timing of the optical switching processor, to correct a time difference between the switching timing and the arrival timing; characterised in that the time difference corrector is adapted to affix, to each of a head and a tail of the optical dummy packets, position detection information by means of which synchrony of the optical dummy packets is detected, and the time difference corrector is adapted to, if the position detection information detected from the returned dummy packets show synchrony, to judge that the timing of arrival of the optical dummy packets at the optical switching processor is synchronized with the switching timing of the optical switching processor.