An optical network system that comprises a ring optical network that performs optical transmission by means of wavelength multiplexing, the optical network system comprising: a master node; and a plurality of optical switch nodes (101B-101D), wherein the master node, which is configured to not only act as one of the optical switch nodes in the optical network but also to control the optical networks, is configured to divide a wavelength path having an arbitrary wavelength into time slots each having a prescribed time period, and allocate the time slots to each of the optical switch nodes (101B-101D), and wherein each of the optical switch nodes (101B-101D) is configured to synchronously transmit or receive a data or perform route switching, the master node is configured to deliver a control signal including a time slot start time and a time stamp to each of the optical switch nodes (101B-101D), upon receipt of the control signal from the master node, each of the optical switch nodes (101B-101D) is configured to synchronize the time slots and thereby transmit or receive a data or perform route switching, based on each common time of each optical switch node (101B-101D) that is determined such that a difference between each common time and the time of the master node is equal to a propagation delay time, the optical network system is characterized in that the master node is further configured to calculate a time offset value of a specific node which is specified from among the plurality of optical switch nodes (101B-101D) and set the calculated time offset value to the specific node, based on the propagation delay time between the master node and each of the plurality of optical switch nodes (101B-101D) and on a propagation delay time for one round on the ring, and each of the optical switch nodes (101B-101D) is configured to: share information on a common time such that each node having a local clock has a time common to all the nodes; upon receipt of the control signal from the master node, synchronize the time slots based on a delay time obtained by subtracting a value of a time stamp from a receipt time of the control signal; and thereby transmit or receive a data or perform route switching; and cause a counter of a first time slot thereon to start a time set by the master node to perform operations of the first time slot starting from the set time, wherein the specific node is configured to cause a counter of a second time slot to start, which is a time slot starting from a timing shifted from a start timing of the first time slot of its own node by the time offset value set by the master node. a master node; and a plurality of optical switch nodes (101B-101D), wherein the master node, which is configured to not only act as one of the optical switch nodes in the optical network but also to control the optical networks, is configured to divide a wavelength path having an arbitrary wavelength into time slots each having a prescribed time period, and allocate the time slots to each of the optical switch nodes (101B-101D), and wherein each of the optical switch nodes (101B-101D) is configured to synchronously transmit or receive a data or perform route switching, the master node is configured to deliver a control signal including a time slot start time and a time stamp to each of the optical switch nodes (101B-101D), upon receipt of the control signal from the master node, each of the optical switch nodes (101B-101D) is configured to synchronize the time slots and thereby transmit or receive a data or perform route switching, based on each common time of each optical switch node (101B-101D) that is determined such that a difference between each common time and the time of the master node is equal to a propagation delay time, the optical network system is characterized in that the master node is further configured to calculate a time offset value of a specific node which is specified from among the plurality of optical switch nodes (101B-101D) and set the calculated time offset value to the specific node, based on the propagation delay time between the master node and each of the plurality of optical switch nodes (101B-101D) and on a propagation delay time for one round on the ring, and each of the optical switch nodes (101B-101D) is configured to: share information on a common time such that each node having a local clock has a time common to all the nodes; upon receipt of the control signal from the master node, synchronize the time slots based on a delay time obtained by subtracting a value of a time stamp from a receipt time of the control signal; and thereby transmit or receive a data or perform route switching; and cause a counter of a first time slot thereon to start a time set by the master node to perform operations of the first time slot starting from the set time, share information on a common time such that each node having a local clock has a time common to all the nodes; upon receipt of the control signal from the master node, synchronize the time slots based on a delay time obtained by subtracting a value of a time stamp from a receipt time of the control signal; and thereby transmit or receive a data or perform route switching; and cause a counter of a first time slot thereon to start a time set by the master node to perform operations of the first time slot starting from the set time, wherein the specific node is configured to cause a counter of a second time slot to start, which is a time slot starting from a timing shifted from a start timing of the first time slot of its own node by the time offset value set by the master node.