According to one embodiment, a storage device includes a data conversion unit that coverts user data of n bits, into m three-ary symbols, a recording medium that records the symbols as a signal of any one of three levels corresponding to values of the symbols, and a Viterbi equalizer that performs equalization of the m symbols simultaneously based on a signal read from the recording medium while setting the number of states as a power of 3 and using a trellis diagram having 2n branches, and calculates 2n likelihoods.