To evade the tentative interruption of other operations as well as not stopping a communication function even when abnormality occurs in a communication channel.

This communication driver 3 to be operated under a multi-thread OS environment and to be called from an application program 1 through a common function 2 is provided with channels 31D, E and F for backup other than normal communication channels 31A, B and C. For instance, when the abnormality occurs in the normal communication channel 31A, it is switched to the communication channel 31D corresponding to it by the common function 2.