1. A device to reconfigure multi-level logic networks, wherein plural pq elements storing LUTs of subfunctions obtained by the functional decomposition of the objective logic function F(X) with the input variables X, are connected to form a network according to the connection relation among the inputs and outputs of said subfunctions, due to the logic modification that modifies the output vector F(b) of said objective logic function F(x) for the input vector b to “invalid value”, comprising: means to select element that selects pq elements one-by-one from the pq element E G that is in the nearest place to the output terminal, among the unmodified said pq elements; means to check correspondence that checks whether the input vector corresponding to the output vector c exists other than said input vector b, where c denotes the output vector for said input vector b among the output vectors of LUTs of said pq element E G ; and means to modify by deleting a vector that changes the state of said pq element E G as modified, and to rewrite the output vector c for said input vector b to “invalid value”, when said input vector b is the only vector that produces said output vector c in the LUTs of the pq element E G .