  Measurement of the cross-section of e+e- -> ZHH offers the information of the
trilinear Higgs self-coupling, which is important to confirm the mechanism of
the electro-weak symmetry breaking. Since there is huge background in the
signal region, background rejection is key point to identify ZHH events. In
this paper, we study the possibility to observe the ZHH events at ILC by using
ZHH -> nu nu HH, resulting 4 jets.
