In this paper, we show that for each forcing notion P in a transitive model M of ZFC, if P satisfies some conditions, there is an elementary embedding from M into a generic ultrapower contains a P-generic set. And, we also introduce the result that if we assume the existence of some large cardinals, the above generic ultrapower can be well-founded. Using this result, we prove some theorems on the problems of regularity properties of definable sets of reals.