  A rapidly spinning neutron star (NS) would emit a continuous gravitational
wave (GW) detectable by the advanced LIGO, advanced Virgo, KAGRA and proposed
third generation detectors such as the Einstein Telescope (ET). Such a GW does
not propagate freely, but is affected by the Coulomb-type gravitational field
of the NS itself. This effect appears as a phase shift in the GW depending on
the NS mass. We have shown that mass of an isolated NS can, in principle, be
determined if we could detect the continuous GW with two or more frequency
modes. Indeed, our Monte Carlo simulations have demonstrated that mass of a NS
with its ellipticity $10^{-6}$ at 1 kpc is typically measurable with precision
of 20% using the ET, if the NS is precessing or has a pinned superfluid core
and emits GWs with once and twice the spin frequencies. After briefly
explaining our idea and results, this paper concerns with the effect of
misalignment angle ("wobble angle" in the case of a precessing NS) on the mass
measurement precision.
