According to one embodiment, a malfunction predicting unit includes a level reduction unit, a first buffer gate unit, a second buffer gate unit, a comparator unit and a processing unit. The level reduction unit reduces an input digital signal to generate a level-reduced signal. The first buffer gate unit generates a first output signal. The first output signal has first or second level if the digital signal is or is not higher than a preset threshold level, respectively. The second buffer gate unit generates a second output signal. The second output signal has the first or second level if the level-reduced signal is or is not higher than the preset threshold level, respectively. The comparator unit compares the first and second output signals to generate a comparison result. The processing unit determines whether a malfunction will soon occur, based on the comparison result.