An optical transceiver includes an optical transmitter, an optical receiver, a first processing unit for controlling a section of the optical transmission circuit, a second processing unit for controlling a section of the optical reception circuit, and a signal line. First and second memory regions constitute a MDIO register space. The selection signal is set to a first level when the first memory region includes a MDIO register, and alternatively is set to a second level when the second memory region includes the MDIO register. The first processing unit responds to another MDIO frame having an OP code set to other than “00h” when the selection signal is at the first level, and the second processing unit alternatively responds to the another MDIO frame when the selection signal is at the second level.