PURPOSE: To make it possible to perform smoothly insertion and drawing-out of a unit as well as to reduce wear of a plating on the friction surface of the unit at the time of the insertion and drawing-out.

CONSTITUTION: The title insertion structure is constituted in such a way that a plurality of pieces of support means 1, which are respectively formed in such a way that a driving body 1b is pinched between one end and one end of one pair of support legs 1a and is pivotally attached to the legs 1a, are pinched between guide rails 4a in the plate thickness of one side edge of a unit 2 and are attached to the rails 4a, each support means 1 is inserted in grooves 4a-1 in the guide rails 4a of a shelf 4, the respective outer side surfaces of the one pair of the support legs are guided to the side-wall surfaces of the guide rails, the driving body is rolled on the bottoms of the grooves and is inserted or drawn out. Or the insertion structure is constituted in such a way that the respective inner side surfaces of the one pair of the support legs 1a are guided to the sidewall surfaces of the rails and the driving body is rolled on the upper surfaces of the sidewalls of the guide rails and inserted or drawn out.