An image capturing apparatus to which a lens unit having an optical imaging system is attachable, comprising: an image sensor configured to generate an image signal by performing photoelectric conversion on a light flux passing through the optical imaging system; a first calculation unit configured to obtain first control information for focus control by using a signal output from the image sensor; and a second calculation unit configured to obtain second control information for focus control without using a signal output from the image sensor, and transmit the second control information to the lens unit. The first calculation unit transmits the first control information to the lens unit without mediation of the second calculation unit.