  I investigate entanglement entropy of one dimension (1D) cluster states to
discuss the delocalization of clusters in linear-chain $3\alpha$- and
$4\alpha$-cluster states. In analysis of entanglement entropy of 1D
Tohsaki-Horiuchi-Schuck-R\"opke (THSR) and Brink-Bloch cluster wave functions,
I show clear differences in the entanglement entropy between localized cluster
wave functions and delocalized cluster wave functions. In order to clarify
spatial regions where the entanglement entropy is generated by the
delocalization of clusters, I analyze the spatial distribution of entanglement
entropy. In the linear-chain $3\alpha$ cluster state, the delocalization occurs
dominantly in a low-density tail region while it is relatively suppressed in an
inner region because of Pauli blocking effect between clusters. In the
linear-chain 4$\alpha$ state having a larger system size than the linear-chain
$3\alpha$ state, the delocalization occurs in the whole system. The
entanglement entropy is found to be a measure of the delocalization of clusters
in the 1D cluster systems.
