A fiber optic communication system comprising: an arrayed waveguide grating, AWG, that has N optical input ports (1-201 to 1-205), where N is an integer greater than or equal to 2, and N optical output ports, and that has a routing function that outputs to predetermined optical output ports (3-51a to 3-51h) in accordance with a wavelength of optical signals inputted to respective optical input ports (1-201 to 1-205), and further comprising M, where M is an integer no smaller than 2, nor greater than the integer N, network-node equipments (2-301 to 2-304) each of said M network-node equipments having an optical input port and an optical output port, an optical output port of said AWG and an optical input port of each of said M network-node equipments (2-301 to 2-304), and an optical input port of said AWG and an optical output port of each of said M network-node equipments (2-301 to 2-304) being connected respectively via optical transmission paths so as to form a geometrically star-shaped physical star topology having the AWG in the center, and wherein each of said M network-node equipments (2-301 to 2-304) further comprise a wavelength tunable light source unit (4-1301 to 4-1303) and a wavelength switching device that switches the wavelength of said optical signals in order to dynamically change a logical network topology that indicates a geometrical form of routes of the optical signals used for transmitting/receiving data, hereafter referred to as optical signals, between said M network-node equipments (2-301 to 305), and wherein the fiber optic communication system further comprises a central-management-equipment, and wherein said central-management-equipment includes a controlling device that transmits to said M network-node equipments (2-301 to 2-304) a first control signal that includes first information of changing wavelength, and that receives a second control signal that includes second information of communication status from said M network-node equipments (2-301 to 2-304), the first information being for changing the logical network topology from a first logical network topology to a second logical network topology which is different from the first logical network topology, and, said wavelength switching device of each of the M network-node equipments (2-301 to 2-304) changes the logical network topology from the first logical network topology to the second logical network topology by switching the wavelength of an optical signal based on said first control signal received from said central-management-equipment. an arrayed waveguide grating, AWG, that has N optical input ports (1-201 to 1-205), where N is an integer greater than or equal to 2, and N optical output ports, and that has a routing function that outputs to predetermined optical output ports (3-51a to 3-51h) in accordance with a wavelength of optical signals inputted to respective optical input ports (1-201 to 1-205), and further comprising M, where M is an integer no smaller than 2, nor greater than the integer N, network-node equipments (2-301 to 2-304) each of said M network-node equipments having an optical input port and an optical output port, an optical output port of said AWG and an optical input port of each of said M network-node equipments (2-301 to 2-304), and an optical input port of said AWG and an optical output port of each of said M network-node equipments (2-301 to 2-304) being connected respectively via optical transmission paths so as to form a geometrically star-shaped physical star topology having the AWG in the center, and wherein each of said M network-node equipments (2-301 to 2-304) further comprise a wavelength tunable light source unit (4-1301 to 4-1303) and a wavelength switching device that switches the wavelength of said optical signals in order to dynamically change a logical network topology that indicates a geometrical form of routes of the optical signals used for transmitting/receiving data, hereafter referred to as optical signals, between said M network-node equipments (2-301 to 305), and wherein the fiber optic communication system further comprises a central-management-equipment, and wherein said central-management-equipment includes a controlling device that transmits to said M network-node equipments (2-301 to 2-304) a first control signal that includes first information of changing wavelength, and that receives a second control signal that includes second information of communication status from said M network-node equipments (2-301 to 2-304), the first information being for changing the logical network topology from a first logical network topology to a second logical network topology which is different from the first logical network topology, and, said wavelength switching device of each of the M network-node equipments (2-301 to 2-304) changes the logical network topology from the first logical network topology to the second logical network topology by switching the wavelength of an optical signal based on said first control signal received from said central-management-equipment.