In communication between communication terminals utilizing a network, a communication apparatus that receives and interprets service contents information described by a tag-type language or the like and performs processing in accordance with the interpretation thereof is disposed between the communication terminals. The communication apparatus can combine a plurality of processing operations in accordance with the described contents of the information to be implemented and can make various service designs. Further, the communication apparatus is characterized to acquire a program for updating a processing method definition connecting the service contents information and the processing operations by means of the Internet so that the processing method definition of the apparatuses distributed dispersedly can be modified promptly and the whole system can cope with modification of service contents promptly.