PURPOSE: To provide the data processing terminal equipment coping quickly with diversified request from the user with respect to an input and an output device and improving the maintenance performance.

CONSTITUTION: On the occurrence of an external interrupt signal, whether the external interrupt signal relates an input output device to be connected or an input output device not connected, that is, whether or not the external interrupt signal is an illegal interrupt is discriminated (ST1), and whether or not the processing under execution is a self-diagnosis processing is discriminated (ST3), and when the interrupt is an illegal interrupt caused during self-diagnosis execution processing, a message corresponding to the external interrupt signal stored in a message memory is extracted (ST4) and outputted to a connected output device (ST5).