There is a provided a semiconductor device having a high security whose power consumption is difficult to analyze even without setting up random characteristic to the processing time. The semiconductor device includes a target circuit (14), a sub-target circuit (15) having the same circuit configuration as the target circuit (14), and a dummy bit string generation circuit (11) for generating a bit string of a dummy serial input signal to be inputted to the sub-target circuit (15) according to the bit string of the serial input signal of the target circuit (14). The dummy bit string generation circuit (11) includes a hamming distance detection circuit (12) for detecting a hamming distance between two continuous bits of the serial input signal as a first hamming distance, and a conflicting signal generation circuit (13) for generating after the last bit, upon detection of the first hamming distance, an input bit having a hamming distance from the last bit of the bit string of the dummy serial input signal which distance is a second hamming distance conflicting with the first hamming distance.