Provided are a communication processing device and a communication system, capable of securely updating a communication protocol process with a simple configuration and technique, while continuing communication. A communication processing device, which is connected to a communication network, includes a programmable logic device in which partial rewriting of a logic circuit is possible, during an operation of a host device in the communication network, in which the programmable logic device includes at least two communication processing circuits of which each performs a communication protocol process, and in which one communication processing circuit is operable due to switching, a first communication processing circuit performs communication, and a second communication processing circuit is on standby, updating means for downloading logic circuit data of an updated communication protocol process, from the communication network, and performing a circuit configuration for the second communication processing circuit, a flag that indicates whether or not the circuit configuration for the second communication processing circuit is finished, and by which a circuit configuration state is able to be read to the host device side through communication, and a register that is intended for switching to any one communication processing circuit to be used, and is writable from the host device side through communication.