To provide a rattling preventive tool superior in durability and versatility of slidable fittings.

This rattling preventive tool is composed of a fixed housing M having the specific depth S1 embedded in an upper end neck part 2 of the slidable fittings D and a pair of symmetric front-back movable blades A forming a substantially inverted L shape inserted and set in its inside; and is determined so as to naturally absorb clearance between a groove rail 1 and the neck part 2, by elastically pressingly energizing a leaf 9 to the groove rail 1 of a door lintel B in a strutting-expansively opening state, by respectively inserting and arranging a first compression coil spring 15 between mutual facing ones of mutual installation leg plates 10 and a second compression coil spring 17 between mutual facing ones of mutual substantially horizontal leaves 9, by respectively rotatably pivoting a lower end part of the installation leg plates 10 in its movable blades A on a horizontal fulcrum rib 7 on the housing M side.