Abstract: In an electronic cash register mutual transmission system, a plurality of electronic cash registers each having a memory for storing total data are electrically connected to each other. A search is made to confirm whether the classified sales data storage area is present in the memory of an electronic cash register which corresponds to the classified data inputted from another of the electronic cash registers. If it is present, the summing is performed in the memory of the former electronic cash register. If it is absent, the classification data is transmitted to another electronic cash register. The former electronic cash register outputs a request signal for data transfer to other electronic cash registers. In response to this request signal, the other electronic cash registers transfer the total data for printing by the former electronic cash register.