Apparatus for a scaffold having scaffolding levels (49, 50, 52) with vertical members, bars, boards and guard rails for mounting a necessary and temporarily present guard rail of an existing scaffolding level for a scaffolding level that is yet to be constructed and is to be mounted thereabove, having - a rail support (12, 200, 300) that is connectable to the front side of a vertical member of the existing scaffolding level and has - a first connection device, - a second connection device, - a third connection device, wherein - the first connection device is arranged in the upper end region of the rail support (12, 200, 300) and serves for connecting the temporary guard rail, - the third connection device is configured such that it is releasably connectable to the mounted vertical member of the existing level in the region of the connection of the mounted guard rail and the spacing between the third connection device and the first connection device is selected such that, with the third connection device connected, the temporary guard rail is at a predefined height with regard to the scaffolding level yet to be constructed, - the second connection device is positioned between the first and third connection devices (14, 90') for releasable connection to the vertical member, - means for releasably locking the second and third connection devices are present, - means for actuating the means for releasable locking are present and have, in the upper and/or lower end region of the rail support (12, 200, 300), a handle, in particular a hand grip, a rotary profile which is connected to the handle and is mounted so as to be rotatable within the rail support (12, 200, 300) about a rotation axis, - characterized in that - the second and third connection devices (90, 90') have a U-shaped receiving region that is open towards the front, that is to say perpendicularly to the rotation axis, and the means for releasable locking have a lever element that is subjected to the effect of an elastic element and constricts the U-shaped receiving region for the purpose of locking and opens it for the purpose of releasing, such that the second and third connection devices (90, 90') are connectable to the vertical member in a movably releasable manner from the front, that is to say perpendicularly to the plane formed by the rail supports (12, 200, 300), arrangeable adjacently on the scaffold, and the temporary guard rail, wherein - the lever element is formed so as to be rotatable about a rotation axis and - the means for releasable locking have a cable pull connected to the rotary profile and to the lever element, wherein the lever element is rotatable counter to the effect of the elastic element by rotation of the handle. - a rail support (12, 200, 300) that is connectable to the front side of a vertical member of the existing scaffolding level and has - a first connection device, - a second connection device, - a third connection device, wherein - the first connection device is arranged in the upper end region of the rail support (12, 200, 300) and serves for connecting the temporary guard rail, - the third connection device is configured such that it is releasably connectable to the mounted vertical member of the existing level in the region of the connection of the mounted guard rail and the spacing between the third connection device and the first connection device is selected such that, with the third connection device connected, the temporary guard rail is at a predefined height with regard to the scaffolding level yet to be constructed, - the second connection device is positioned between the first and third connection devices (14, 90') for releasable connection to the vertical member, - means for releasably locking the second and third connection devices are present, - means for actuating the means for releasable locking are present and have, in the upper and/or lower end region of the rail support (12, 200, 300), a handle, in particular a hand grip, a rotary profile which is connected to the handle and is mounted so as to be rotatable within the rail support (12, 200, 300) about a rotation axis, - characterized in that - the second and third connection devices (90, 90') have a U-shaped receiving region that is open towards the front, that is to say perpendicularly to the rotation axis, and the means for releasable locking have a lever element that is subjected to the effect of an elastic element and constricts the U-shaped receiving region for the purpose of locking and opens it for the purpose of releasing, such that the second and third connection devices (90, 90') are connectable to the vertical member in a movably releasable manner from the front, that is to say perpendicularly to the plane formed by the rail supports (12, 200, 300), arrangeable adjacently on the scaffold, and the temporary guard rail, wherein - the lever element is formed so as to be rotatable about a rotation axis and - the means for releasable locking have a cable pull connected to the rotary profile and to the lever element, wherein the lever element is rotatable counter to the effect of the elastic element by rotation of the handle.