A mount adapter includes: a camera cone having a length of adjusting a flange focal length between an imaging device provided with an imaging element and an interchangeable lens; a focus detection unit carrying out focus detection from a phase difference; an optical device separating an incident light from the interchangeable lens into an incident light of the imaging element and an incident light of the focus detection unit; and a correction information storage unit storing correction information used for correction of an error between the flange focal length and a distance from a mounting surface of the interchangeable lens to the focus detection unit.