In a system having a plurality of apparatuses connected via a communication line, one apparatus serving as a master unit performs processing on data stored in the other apparatus or apparatuses. The apparatus serving as a master unit generates a work designation message containing a program statement and transmits it to the other apparatuses. The apparatus, receiving the message, performs data processing based on the message and transfers the message to another apparatus in a predetermined order. All the apparatuses connected to the communication line perform processing based on a received message and the processing is completed when the message is returned back to the master unit.