An idle pattern output-control circuit used in a point-to-multipoint communication based Gigabit Ethernet-passive optical network (GE-PON) is provided. In a GE-PON having an optical-line terminal (OLT), a plurality of optical-network units (ONUs) connected to each other via an optical-distribution network (ODN), a media-access controller (MAC), and a physical-coding sublayer (PCS), in which the PCS transmits idle-pattern data to a serializer/deserializer (SERDES) when there is no data to be transmitted to the OLT, an idle-pattern output-control circuit comprising a data converter for converting an idle-pattern data generated from the PCS into a low-level optical signal for subsequent transmission to the OLT, and a switching circuit for selecting data generated from the PCS for subsequent transmission to the SERDES when there is data to be transmitted and for selecting data converted by the data converter for subsequent transmission to the SERDES when there is no data to be transmitted.