To provide an intertruss bracing device for a casing for drilling, by which the positioning centering works of the casing for drilling and the correction works of the place of drilling at a time when the front end of the casing for drilling collides with an underground obstruction and the place of drilling is changed are conducted easily and rapidlly in case of not only ground works but also marine works.

An arm 11 expansion-contraction driven by an incorporated first fluid-pressure cylinder 14A is attached pivotally to a cylindrical member 8 detachably connected at the lower end of a leader 1 in a rockable manner in the periphery of an axial center parallel with the axial center of the cylindrical member 8. A second fluid-pressure cylinder 14B rocking and driving an arm 11 is installed between a stay 15 continuously connected to the cylindrical member 8 and the arm 11, a cylindrical guide member 19 capable of being opened and closed is coupled continuously at the front end of the arm 11, and the casing 2 for drilling is inserted to a cylindrical guide member 19 and the bracing of the above-mentioned casing for drilling is conducted.