  We report a discovery of a companion candidate around one of {\it Kepler}
Objects of Interest (KOIs), KOI-94, and results of our quantitative
investigation of the possibility that planetary candidates around KOI-94 are
false positives. KOI-94 has a planetary system in which four planetary
detections have been reported by {\it Kepler}, suggesting that this system is
intriguing to study the dynamical evolutions of planets. However, while two of
those detections (KOI-94.01 and 03) have been made robust by previous
observations, the others (KOI-94.02 and 04) are marginal detections, for which
future confirmations with various techniques are required. We have conducted
high-contrast direct imaging observations with Subaru/HiCIAO in $H$ band and
detected a faint object located at a separation of $\sim0.6''$ from KOI-94. The
object has a contrast of $\sim 1\times 10^{-3}$ in $H$ band, and corresponds to
an M type star on the assumption that the object is at the same distance of
KOI-94. Based on our analysis, KOI-94.02 is likely to be a real planet because
of its transit depth, while KOI-94.04 can be a false positive due to the
companion candidate. The success in detecting the companion candidate suggests
that high-contrast direct imaging observations are important keys to examine
false positives of KOIs. On the other hand, our transit light curve reanalyses
lead to a better period estimate of KOI-94.04 than that on the KOI catalogue
and show that the planetary candidate has the same limb darkening parameter
value as the other planetary candidates in the KOI-94 system, suggesting that
KOI-94.04 is also a real planet in the system.
