1. A measurement device comprising: a first measurement unit configured to measure first biological data at least k times, where k≧2, to obtain any k first measurement values; a distributed-signature generation unit configured to execute signature operations for the k first measurement values using any various k distributed-signature keys, respectively, to generate k distributed signatures, the k distributed-signature keys being capable of reconstructing a signature generation key only when all of the k distributed-signature keys are available; a signature synthesis unit configured to synthesize the k distributed signatures together to reconstruct a signature; and a steady state verification unit configured to verify, using a signature verification key corresponding to the signature generation key, whether or not the signature reconstructed by said signature synthesis unit is correct, where the correctness of the signature means that the k first measurement values are same values.