An optical cable, comprising: a transmission connector connected, via the optical cable, to a reception connector, the transmission connector comprising: a transmission optical module having a signal electrode, into which an electric signal is inputted through the signal electrode, and outputting to the optical cable an optical signal converted from the electric signal in the transmission optical module; a transmission receptacle having a contact to be electrically connected to the signal electrode when fitted to the transmission optical module; the reception connector comprising: a reception optical module having a signal electrode, into which an optical signal is inputted from the optical cable, and outputting through the signal electrode an electric signal converted from the optical signal in the reception optical module; a reception receptacle having a contact to be electrically connected to the signal electrode when fitted to the reception optical module; the optical cable further comprising an erroneous fitting prevention arrangement provided in each one of the transmission optical module, the reception optical module, the transmission receptacle, and the reception receptacle, the erroneous fitting prevention arrangement preventing erroneous fitting of the transmission optical module and the reception receptacle as well as erroneous fitting of the reception optical module and the transmission receptacle, characterized in that the erroneous fitting prevention arrangement includes: a first cutout and a second cutout formed on opposing sides in the transmission optical module, the first cutout being formed longer than the second cutout; a first projection formed on one side in the transmission receptacle to be fitted in the first cutout when the transmission optical module is fitted to the transmission receptacle; a first cutout and a second cutout formed on opposing sides in the reception optical module, the second cutout being formed longer than the first cutout; and a second projection formed on one side in the reception receptacle to be fitted in the second cutout when the reception optical module is fitted to the reception receptacle; wherein the opposing sides are inversed between the transmission optical module and the reception optical module. a transmission optical module having a signal electrode, into which an electric signal is inputted through the signal electrode, and outputting to the optical cable an optical signal converted from the electric signal in the transmission optical module; a transmission receptacle having a contact to be electrically connected to the signal electrode when fitted to the transmission optical module; a reception optical module having a signal electrode, into which an optical signal is inputted from the optical cable, and outputting through the signal electrode an electric signal converted from the optical signal in the reception optical module; a reception receptacle having a contact to be electrically connected to the signal electrode when fitted to the reception optical module; the optical cable further comprising an erroneous fitting prevention arrangement provided in each one of the transmission optical module, the reception optical module, the transmission receptacle, and the reception receptacle, the erroneous fitting prevention arrangement preventing erroneous fitting of the transmission optical module and the reception receptacle as well as erroneous fitting of the reception optical module and the transmission receptacle, characterized in that the erroneous fitting prevention arrangement includes: a first cutout and a second cutout formed on opposing sides in the transmission optical module, the first cutout being formed longer than the second cutout; a first projection formed on one side in the transmission receptacle to be fitted in the first cutout when the transmission optical module is fitted to the transmission receptacle; a first cutout and a second cutout formed on opposing sides in the reception optical module, the second cutout being formed longer than the first cutout; and a second projection formed on one side in the reception receptacle to be fitted in the second cutout when the reception optical module is fitted to the reception receptacle; wherein the opposing sides are inversed between the transmission optical module and the reception optical module. a first cutout and a second cutout formed on opposing sides in the transmission optical module, the first cutout being formed longer than the second cutout; a first projection formed on one side in the transmission receptacle to be fitted in the first cutout when the transmission optical module is fitted to the transmission receptacle; a first cutout and a second cutout formed on opposing sides in the reception optical module, the second cutout being formed longer than the first cutout; and a second projection formed on one side in the reception receptacle to be fitted in the second cutout when the reception optical module is fitted to the reception receptacle; wherein the opposing sides are inversed between the transmission optical module and the reception optical module.