Abstract: An apparatus is disclosed for preventing cave-ins of mining galleries and other underground excavations. It includes a base, a roof-supporting shield extending upwardly from the base and a free edge to which a roof-supporting cap is pivoted, and an advancing arrangement for advancing the apparatus towards and away from a face of the excavation. The advancing arrangement has a shiftable carriage which can move towards and away from this face and which has an end directed towards the latter, and an extension section is telescopable into and out of this end and can be arrested in a plurality of different telescoped positions.