  We present our optical follow-up observations to search for an
electromagnetic counterpart of the first gravitational wave source GW150914 in
the framework of the Japanese collaboration for Gravitational wave
ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing
optical and radio telescopes in Japan, as well as those in New Zealand, China,
South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey
with Kiso Wide Field Camera (KWFC) on the 1.05-m Kiso Schmidt telescope in
Japan and a galaxy-targeted survey with Tripole5 on the B&C 61-cm telescope in
New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band
with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and
i-bands 4-12 days after the gravitational wave detection. Median 5-sigma depths
are i~18.9 mag for the KWFC data and g~18.9 mag, r~18.7 mag, and i~18.3 mag for
the Tripole5 data. Probability for a counterpart to be in the observed area is
1.2% in the initial skymap and 0.1% in the final skymap. We do not find any
transient source associated to an external galaxy with spatial offset from its
center, which is consistent with the local supernova rate. We summarize future
prospects and ongoing efforts to pin down electromagnetic counterparts of
binary black hole mergers as well as neutron star mergers.
