The first object of the present invention is to provide a derailment prevention guard which can be easily shunted outside the range of the ballast tamping work, the rail grinding work and the rail maintenance work, and has no problem on safety.A derailment prevention guard comprises a guard member installed within a gauge and a support member fixed to a sleeper or a concrete slab track, and the guard member is held by a hold member which can turn around a central axis supported by the support member as turning center between a main rail and the inside of the gauge on the sleeper or the concrete slab track, and the support member is engaged with the hold member by means of a bolt through turning the hold member toward the main rail around the central axis as turning center on the sleeper or the concrete slab track, and the guard member can be shunted inward within the gauge by turning the hold member toward the inside of the gauge around the central axis as turning center on the sleeper or the concrete slab track after loosening the bolt.