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We report a discovery of a companion candidate around one of {\it Kepler}Objects of Interest (KOIs), KOI-94, and results of our quantitativeinvestigation of the possibility that planetary candidates around KOI-94 arefalse positives. KOI-94 has a planetary system in which four planetarydetections have been reported by {\it Kepler}, suggesting that this system isintriguing to study the dynamical evolutions of planets. However, while two ofthose detections (KOI-94.01 and 03) have been made robust by previousobservations, the others (KOI-94.02 and 04) are marginal detections, for whichfuture confirmations with various techniques are required. We have conductedhigh-contrast direct imaging observations with Subaru/HiCIAO in $H$ band anddetected a faint object located at a separation of $\sim0.6''$ from KOI-94. Theobject has a contrast of $\sim 1\times 10^{-3}$ in $H$ band, and corresponds toan M type star on the assumption that the object is at the same distance ofKOI-94. Based on our analysis, KOI-94.02 is likely to be a real planet becauseof its transit depth, while KOI-94.04 can be a false positive due to thecompanion candidate. The success in detecting the companion candidate suggeststhat high-contrast direct imaging observations are important keys to examinefalse positives of KOIs. On the other hand, our transit light curve reanalyseslead to a better period estimate of KOI-94.04 than that on the KOI catalogueand show that the planetary candidate has the same limb darkening parametervalue as the other planetary candidates in the KOI-94 system, suggesting thatKOI-94.04 is also a real planet in the system.

A Discovery of a Candidate Companion to a Transiting System KOI-94: A Direct Imaging Study for a Possibility of a False Positive