An optical communication device configured to communicate with a first optical communication device , comprising: a conversion unit configured to receive an optical signal transmitted from the first optical communication device and convert the optical signal into a digital electric signal based on a clock signal; a clock switching unit configured to switch an oscillator generating the clock signal; an operation mode control unit configured to detect an operation mode of the first optical communication device in the digital electric signal and command the clock switching unit to perform switching from the oscillator generating the clock signal to an oscillator generating a clock signal at a frequency based on the operation mode of the first optical communication device ; and a storage unit configured to store a previously set operation mode, characterized in that when a baud rate represented by the operation mode stored in the storage unit is higher than a baud rate represented by the operation mode of the first optical communication device , the operation mode control unit changes the baud rate represented by the operation mode stored in the storage unit to the baud rate represented by the operation mode of the first optical communication device and commands the clock switching unit to perform switching from the oscillator generating the clock signal to an oscillator generating a clock signal at a frequency based on the baud rate represented by the operation mode after the change, and wherein when the baud rate represented by the operation mode stored in the storage unit is lower than the baud rate represented by the operation mode of the first optical communication device , the operation mode control unit performs control so as not to change the baud rate represented by the operation mode stored in the storage unit to the baud rate represented by the operation mode of the first optical communication device . a conversion unit configured to receive an optical signal transmitted from the first optical communication device and convert the optical signal into a digital electric signal based on a clock signal; a clock switching unit configured to switch an oscillator generating the clock signal; an operation mode control unit configured to detect an operation mode of the first optical communication device in the digital electric signal and command the clock switching unit to perform switching from the oscillator generating the clock signal to an oscillator generating a clock signal at a frequency based on the operation mode of the first optical communication device ; and a storage unit configured to store a previously set operation mode, characterized in that when a baud rate represented by the operation mode stored in the storage unit is higher than a baud rate represented by the operation mode of the first optical communication device , the operation mode control unit changes the baud rate represented by the operation mode stored in the storage unit to the baud rate represented by the operation mode of the first optical communication device and commands the clock switching unit to perform switching from the oscillator generating the clock signal to an oscillator generating a clock signal at a frequency based on the baud rate represented by the operation mode after the change, and wherein when the baud rate represented by the operation mode stored in the storage unit is lower than the baud rate represented by the operation mode of the first optical communication device , the operation mode control unit performs control so as not to change the baud rate represented by the operation mode stored in the storage unit to the baud rate represented by the operation mode of the first optical communication device . <EOS>