Observation of exoplanet atmospheres enables us to test and improve the models of planetary atmosphere. Furthermore, this is important for the characterization of exoplanets, which leads to explore their formation and evolution scenarios. Among the techniques to observe exoplanets, direct imaging is currently the most efficient to find and characterize wide-orbit (> ~10 AU) giant planets. In addition, this technique allows for tracing the planet's energy distribution as a function of wavelengths. Indeed, the wide-orbit planets have been discovered with this technique, providing new insights into the exoplanet atmospheres. We have carried out an extensive campaign, SEEDS, to search for wide-orbit exoplanets. This campaign has finished about 120-night observations. We have selected the target samples from nearby field stars and young stars that are associated to moving groups, the Pleiades open cluster, or star forming regions. As a result, it was revealed that the G0-type star GJ 504 has a significantly faint companion (GJ 504b). Based on our age estimate (100–510 Myr) for GJ 504 and theoretical evolution models for giant planets, the companion's mass is calculated to be 3–8.5 Jupiter masses. Furthermore, using the similar way, we inferred its effective temperature to be ~500 K, being consistent to the observed evidence of methane in its atmosphere. We also detected a massive giant planet or brown dwarf companion orbiting the nearby B-type star Kapp And. We here report the SEEDS direct imaging studies for giant exoplanets; then, we place emphasis on the atmosphere studies in our observations.