In a computer network system comprising a plurality of computers connected to a communication line, each computer executes a program including a function. In one of the computers, a judging section is supplied with a request indicative of the function from the program and judges whether or not the function can be executed by the above-mentioned one to produce a non-executable signal when the function cannot be executed by the above-mentioned one. Responsive to the non-executable signal, a request command generating section generates an original request command which is transmitted to at least one other computer as a transmission request command by a command transmitting section. A command receiving section of the other computer receives the transmission request command as a received request command, which an executing section executes to produce an execution result generated by a reply command generating section as an original reply command transmitted by the command transmitting section as a transmission reply command back to the above-mentioned one. The command receiving section of the above-mentioned one receives the transmission reply command as a received reply command which is returned to the program as the execution result by a returning section.