To provide drain culvert forming apparatus which carries out guide ditch forming work and drain culvert forming work by the same apparatus and allows the smooth advance of an excavating body along a guide ditch.

The drain culvert forming apparatus covering a flexible underdrainage pipe laid while delivering the underdrainage pipe after forming the guide ditch, with a hydrophobic material includes a hydrophobic material supply chute 2 supplying the hydrophobic material onto the underdrainage pipe, and an excavating body 3 cutting soil open to form a ditch, wherein the hydrophobic material supply chute and the excavating body are integrally provided. A tubular underdrainage pipe guide part 13 for guiding and delivering the underdrainage pipe into the ditch is provided at the rear part of the excavating body 3, and a mounting member 5 mounted to an arm of a backhoe is connected to the upper part of the excavating body through a rotating part 6 capable of rotating the direction of the excavating body 3 into a position opposite by 180°.