I will briefly review our effort to understand the coevolution of supermassive black holes and their host galaxies. To tackle this issue, we use the images of type I active galactic nuclei (AGN) obtained from the Hubble Space Telescope. We find that star formation activity in the host galaxy is closely connected with the luminosity of AGN. However, the fraction of young stars to AGN luminosity appears to be saturated at high accretion rates, revealing that AGN feedback may play an important role in regulating star formation in luminous AGNs. In the second of my talk, I will present a multiwavelength study of an ultraluminous X-ray source (ULX) in NGC 5252, which is known as a candidate for an intermediate-mass black hole. The ULX, located 22 arcsec away from the center of NGC 5252, was first discovered with the Chandra X-Ray Observatory. From the multiwavelength data, we find that the ULX is associated with the host galaxy and the ULX may be a remnant of a merging dwarf galaxy.