A communication device comprising: a communication section (31-4) that configured to transmit , as a batch of data blocks (DB), an SPI (Serial Peripheral Interface)-compliant serial signal group transmitted from a Master to the communication section (34-4) in synchronization with a clock (SCK), to a communication partner device within one frame period of a predetermined communication protocol or to transmit the serial signal group as multiple data blocks (DB) divided according to multiple frame periods of the predetermined communication protocol, to the communication partner device a memory (31-1-2) that is configured to save an SPI-compliant first serial signal group transmitted from the Master in synchronization with the clock (SCK) and to save an SPI-compliant second serial signal group transmitted from a Slave in synchronization with the clock (SCK); a packet encoder (31-2) that is configured to convert the first serial signal group saved in the memory (31-1-2) into a first packet of the predetermined communication protocol, wherein the first packet includes frequency information regarding the clock; and a packet decoder (31-3) that is configured to convert a second packet of the predetermined communication protocol received from the communication partner device into the second serial signal group; wherein the communication section (31-4) is configured to transmit the first packet to and to receive the second packet from the communication partner device by the predetermined communication protocol according to TDD (Time Division Duplex) or according to FDD (Frequency Division Duplex). a communication section (31-4) that configured to transmit , as a batch of data blocks (DB), an SPI (Serial Peripheral Interface)-compliant serial signal group transmitted from a Master to the communication section (34-4) in synchronization with a clock (SCK), to a communication partner device within one frame period of a predetermined communication protocol or to transmit the serial signal group as multiple data blocks (DB) divided according to multiple frame periods of the predetermined communication protocol, to the communication partner device a memory (31-1-2) that is configured to save an SPI-compliant first serial signal group transmitted from the Master in synchronization with the clock (SCK) and to save an SPI-compliant second serial signal group transmitted from a Slave in synchronization with the clock (SCK); a packet encoder (31-2) that is configured to convert the first serial signal group saved in the memory (31-1-2) into a first packet of the predetermined communication protocol, wherein the first packet includes frequency information regarding the clock; and a packet decoder (31-3) that is configured to convert a second packet of the predetermined communication protocol received from the communication partner device into the second serial signal group; wherein the communication section (31-4) is configured to transmit the first packet to and to receive the second packet from the communication partner device by the predetermined communication protocol according to TDD (Time Division Duplex) or according to FDD (Frequency Division Duplex). <EOS>