  We show how entangled valence-bond singlet pairs are disentangled partially
and totally by the Kennedy-Tasaki transformation which reveals the hidden
$Z_2\times Z_2$ symmetry in valence-bond-solid chains as a higher-spin
generalization of the previous studies toward the intermediate-$D$ state. The
totally disentangled states correspond to four Ising-like states with $Z_2$
variables on the boundary. We present a simple expression of results by using
the spin decomposition and the boundary matrix.
