A focus detection device includes: an image capture unit that has a plurality of light receiving units provided for each of a plurality of micro lenses, and that captures image by light from a subject that has passed through an optical system; and a focus detection unit that detects a focusing state of the optical system according to a relative positional deviation of the images of the subject with respect to the micro lenses, with the image of the subject being created by each of the micro lenses and being captured by the image capture unit.