PURPOSE: To decrease the number of interruption to a CPU and to reduce the load of CPU, by automatically returning EOT information to general polling with a channel incorporated type of communication controller.

CONSTITUTION: When a power supply non-applicated state or a busy state takes place in a CPU 21, a chained command train is prepared to generate a start I/O instruction. When a channel incorporated type of communication controller 23 receives a read command, the polling wait state is obtained and when the polling is received, it is discriminated whether the polling is specific polling (S-Poll) or a general polling (G-Foll). In case of the G-Poll, a channel end bit in status information and a device end bit are set for interruption. In case of the S-Poll, the device 23 adds the channel end bit to the device end bit to set a unit exception bit for the interruption.