A structure of a detachable front loader includes: a main frame; a boom; and a subframe unit that supports the boom. The subframe unit includes: a subframe; a guide that is disposed on the subframe and engages with the main frame; a lock bar that includes a pivot shaft disposed on the subframe, and a pivot shaft part; an operation tool that moves the lock bar from the restriction position to the release position against a first biasing force; and a locking tool that is supported by the subframe, moves between a locking position and an unlocking position, is biased in a locking direction, and once the operation tool moves the lock bar to the release position, moves to the locking position by a second biasing force, and engages with a cutout formed in the pivot shaft part.