To provide an insert structure with which mounting work can be done by oneself from the outside of a form.

A bolt member (3) is screwed to an insert body (4) by successively inserting a sleeve member (1) and a stopper member (2), the stopper member (2) is placed to the inside of the form (5), the stopper member (2) includes a short cylinder section (20) having a tapered circumferential surface gradually enlarging a diameter in the direction of the inside and a plurality of claw sections (21) gradually heightening the height in the direction of the outside slantingly arranged to the axial center of the short cylinder (20) in a view from the diametrical direction at regular intervals in the circumferential direction on the circumferential surface of the short cylinder section (20), the sleeve member (1) comprises a separate component of at least one common cylinder (10) fitted into a through-hole (5a) of the form (5) and a circular plate section (11) placed to the outside of the form (5), and it is so formed that an integral multiple of the size of a length of the common cylinder section (10) is approximately the same as that of the size of a plate thickness (T) of the form (5).