212 and sets the queue as finished in learning when the onu under switching is set as finished in learning the onu distributor 210 transfers the packet to the switching queue 224 registered on the learning table 212 the control signal generator 260 generates a control signal such as gate signal 24 for use in establishing a pon link switching of the reception wavelength in the onu can be directed by using the control signal 24 the through queue 222 and the plurality of switching queues 224 a to 224 k are responsive to packets when inputted to issue one of corresponding transmission requests 26 and 28 a to 28 k to the scheduler 250 the scheduler 250 is operative in response to a transmission request from the queues 222 and 224 a to 224 k or a request for transmitting a control signal 24 to arrange its output and transmits a downstream signal 18 to the onu via the optical transmitter referring back to fig1 the olt controller 140 controls the entire olt and the osu installed in the olt for instance the olt controller 140 carries out updating of the llid identification table 112 and llid allocation table 122 the olt controller 140 also carries out monitoring of traffic pas sing through the olt and determines the timing and content of the path switching in addition the olt controller 140 monitors readout of the osu from the scheduler 250 moreover when changing the osu on which an onu under switching will be registered the olt controller 140 releases the old osu currently under switching i e the osu having the onu registered so far registers the onu on a new osu to which the registration is to be switched or shifted and notifies the.