  Quantum entanglement is the quantum information processing resource. Thus it
is of importance to understand how much of entanglement particular quantum
states have, and what kinds of laws entanglement and also transformation
between entanglement states subject to. Therefore, it is essentialy important
to use proper measures of entanglement which have nice properties. One of the
major candidates of such measures is "entanglement of formation", and whether
this measurement is additive or not is an important open problem. We aim at
certain states so-called "antisymmetric states" for which the additivity are
not solved as far as we know, and show the additivity for two of them.
  Keywords: quantum entanglement, entanglement of formation, additivity of
entanglement measures, antisymmetric states.
