  With the current precision of measurements by the ATLAS and CMS experiments,
it cannot be excluded that a SM-like Higgs boson is a CP violating mixture of
CP-even and CP-odd states. We explore this possibility here, assuming Higgs
boson production in ZZ-fusion, at 1 TeV ILC, with unpolarized beams. The full
simulation of SM background and fast simulation of the signal is performed,
simulating 8 ab$^{-1}$ of data collected with the ILD detector. We demonstrate
that the CP mixing angle $\Psi_{\mathrm{CP}}$ between scalar and pseudoscalar
states can be measured with the statistical uncertainty of 3.8 mrad at 68% CL,
corresponding to 1.44 $\cdot 10^{-5}$ for the CP parameter $f_\mathrm{CP}$, for
the pure scalar state. This is the first result on sensitivity of an
$e^{+}e^{-}$ collider to measure $f_\mathrm{CP}$ in the Higgs production vertex
in vector boson fusion.
