Abstract: In the case where an external signal line is driven by a circuit other than an output circuit with a voltage higher than an on-chip power-source voltage, if an output transistor is activated in the output state immediately after the driving of the external signal line by the above other circuit was cancelled, a voltage equal to or higher than the breakdown voltage of an oxide film of a transistor composing the output circuit is applied thereto. To prevent this, there is provided a voltage detecting means for detecting a voltage value of the above external signal line being higher than a value in the vicinity of the internal power-source voltage and generating a detection signal, which inhibits the activation of the output transistor.