PURPOSE: To prevent the communication efficient of the communication control system from decreasing even when a processing cell which is connected to a communication line can not be accessed owing to a power break, a fault, etc.

CONSTITUTION: A wait time T is counted up by one (S1) and it is decided whether or not the wait time T exceeds a timeout time Tc; when the wait time T exceeds the timeout time Tc, the wait time T is cleared to '0' and a communication abnormality frequency R(n) is counted up by one (S3 and S4). Then it is decided (S5) whether or not the communication abnormality frequency R(n) exceeds a maximum communication abnormality frequency Rc, and when the communication abnormality frequency R(n) exceeds the maximum communication abnormality frequency Rc, the data link (n) of the corresponding processing cell is logically cut off (S6). Therefore, polling to a processing cell which can not be accessed is not performed, so the communication efficiency is prevented from decreasing.