To provide a bidirectional optical transmitting/receiving device capable of removing an optical crosstalk signal without requiring phase adjustment and amplitude adjustment, and being excellent in receiving characteristic; and to provide a bidirectional optical transmitting system.

The device is provided with a Manchester code encoding circuit 8 for converting a transmission electric signal into a Manchester code; an error correcting circuit 12 for correcting a high level/high level code of a merged electric signal into a high level/low level code if a signal converted by the Manchester code encoding circuit is a low level/high level signal indicating "1", and correcting it into a low level/high level signal if the converted is a high level/low level indicating "0"; and a Manchester code decoding circuit 13 for decoding a code outputted from the error correcting circuit.