A decision method of a 3R relay implementation node in an optical node device that switches an optical signal, the method comprising the step of: defining a preset section in which data transmission is possible without 3R relay as a 3R section, an optical node device at a start point of the 3R section as a 3R source node, an optical node device at an end point of the 3R section as a 3R destination node, an optical node device, being a source of a setting request for an optical path, as a source node, and an optical node device at an end point of the optical path as a destination node; characterized in that the method further comprises, when one optical node device is a 3R source node of any one (3 to 14) of a plurality of different 3R sections (1 to 4, 3 to 14) overlapping on an optical path that passes through the one optical node device, and the one optical node device does not correspond to a 3R source node or 3R destination node of other 3R sections (1 to 4), the steps of comparing (21, 24) the number of 3R implementations for both the case where the one optical node device functions as a 3R source node and where the one optical node device does not function as a 3R source node, with reference to 3R section information related to an optical path (3 to 14) from the one optical node device up to the destination node, and of deciding (21, 23) that the one optical node device is an optical node device that implements 3R relay, when the number of 3R implementations is less in the case where the one optical node device functions as a 3R source node than in the case where the one optical node device does not function as a 3R source node, based on a comparison result. defining a preset section in which data transmission is possible without 3R relay as a 3R section, an optical node device at a start point of the 3R section as a 3R source node, an optical node device at an end point of the 3R section as a 3R destination node, an optical node device, being a source of a setting request for an optical path, as a source node, and an optical node device at an end point of the optical path as a destination node; characterized in that the method further comprises, when one optical node device is a 3R source node of any one (3 to 14) of a plurality of different 3R sections (1 to 4, 3 to 14) overlapping on an optical path that passes through the one optical node device, and the one optical node device does not correspond to a 3R source node or 3R destination node of other 3R sections (1 to 4), the steps of comparing (21, 24) the number of 3R implementations for both the case where the one optical node device functions as a 3R source node and where the one optical node device does not function as a 3R source node, with reference to 3R section information related to an optical path (3 to 14) from the one optical node device up to the destination node, and of deciding (21, 23) that the one optical node device is an optical node device that implements 3R relay, when the number of 3R implementations is less in the case where the one optical node device functions as a 3R source node than in the case where the one optical node device does not function as a 3R source node, based on a comparison result.