Abstract: An optical star network system, wherein a first packet is transmitted between first and second terminals, which are functionally coupled to an optical star network, using a predetermined wavelength band in accordance with the CSMA/CD system, which system comprises a generation section for generating a second packet including transmission data and having a predetermined bit length, and a transmission section for transmitting the second packet on a transmission path using the predetermined wavelength band. The predetermined bit length is set so as not to be equal to an integer multiple of a bit length of a data unit of the first packet. The second packet includes dummy data with the transmission data following this dummy data, the bit length of the dummy data is greater than the bit length of the longest data packet which is to be transmitted before interruption of transmission of the first packet, when the first and second packets collide with each other.