PURPOSE: To facilitate the vertical positioning of a key, rotating work on it and the determination of the insertion length of it in the work for inserting the key into a supporting lattice.

CONSTITUTION: This is a method for inserting a key horizontally after fixing a supporting lattice with a finger block and spreading out its elastic protrusion. A holding jig 3 holds a prescribed length of a tip of a key K. A key inserting orifice 11 is erectly installed parallel to a side of a supporting lattice 1 fixed on a finger block F, and fits and inserts the key K so that it can freely rotate. In a setting plate 10, the key inserting orifice 11 is horizontally drilled so as to coincide with the key-inserting position of the supporting lattice 1. The holding jig 3 and the setting plate 10 are used to position the key K vertically in the supporting lattice 1 by using the height of the key inserting orifice 11 in the setting plate 10. At the same time, the insertion length of the key K is determined by the close contact between the setting plate 10 and the holding jig 3. Afterward, the holding jig 3 is rotated in such a condition to rotate the key K.