Disclosed are an apparatus and a method capable of adjusting an upstream band for a corresponding ONU by detecting a quantity of bands occupied by a packet, not an effective user packet, among upstream transmission bands for each target object of allocation of each band in the OLT to examine whether a queue report is normal, and detecting an ONU, which transmits an abnormal queue report, according to the examination. An OLT of a PON according to an exemplary embodiment of the present disclosure includes: a frame monitoring unit configured to monitor upstream frame data received for each T-CONT; an error detection unit configured to determine whether a queue report error is generated for each T-CONT according to a result of the monitoring; and a band allocation controller configured to allocate an upstream band for an ONU, in which the queue report error is generated, separately from a normal ONU.