A lens adapter is disclosed. The lens adapter includes: an adapter ring having a flexible fitting portion and an installation portion in which an optical component is mounted, the fitting portions being fitted over a fitting engagement portion of a lens ring mounted around a lens portion facing a front surface of an imaging apparatus; and a lock ring fitted over an outer surface of the adapter ring, the lock ring being manipulated so as to be moved between a locked position where the lock ring is opposite to the fitting portions fitted over the fitting engagement portion and flexure of the fitting portions is prevented and an unlocked position where the lock ring is retracted from the locked position.