An inconsistency in shares is detected with a small volume of communications traffic. n inconsistency detecting devices generate random numbers s i and make the random numbers s i public. The n inconsistency detecting devices generate a common random number s which is the sum total of the random numbers s 0 , ..., s n-1 . The n inconsistency detecting devices calculate shares [c] i . The n inconsistency detecting devices generate shares [r] i , each of which would become a random number r by reconstruction. The n inconsistency detecting devices calculate shares [d] i , each of which would become a judgment value d by reconstruction. One inconsistency detecting device receives shares [d] 1 , ..., [d] n-1 from n-1 inconsistency detecting devices. The one inconsistency detecting device restores n-k shares [d]' k , ..., [d]' n-1 from k shares [d] 0 , ..., [d] k-1 . The one inconsistency detecting device judges, for j = k, ..., n-1, whether or not a share [d] j and a share [d]' j coincide with each other.