We have extensively studied the properties of molecular clouds which are associated with the supergiant HII region NGC 604 in the nearest (D = 840 kpc) spiral galaxy M33. We suggest that the dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604 (central OB star cluster) and that giant molecular cloud complex associated with NGC 604 is a unique laboratory for different, especially, for the early and intermediate stages along evolutionary path of star formation in the giant HII region. We present recent results for the Ginat HII regions in M33, including NGC 604.