Using three pieces of element data w1, w2, and w3 obtained by partitioning storage data D, an encryption unit generates three sets of a first set A1 in which the first to third pieces of element data are sequentially arranged, a second set A2 in which the second to third pieces of element data are sequentially arranged, and a third set A3 composed of the third piece of element data. The encryption unit encrypts each piece of element data included in each set with a random number R(1) by a CBC mode.