The invention provides an imaging apparatus and a focus control method in which an optimal AF system can be selected in accordance with an environment in which an image of a photographic subject is taken, an imaging condition in which the image is taken, etc. so that the quality of the taken image can be improved. A system control portion 11 of the imaging apparatus selects and executes one from focus control based on a phase difference AF system and focus control based on a contrast AF system in accordance with the magnitude relation between a determination threshold set for an F-number and the set F-number in the case where an AF instruction has been issued. The system control portion 11 can vary the determination threshold in accordance with an exposure value in the case where the AF instruction has been issued.