Provided are an endoscopic surgical device and an overtube that allows the state of a distal end of a treatment tool to be easily checked while reducing the diameter of the overtube and can improve surgical efficiency, in a configuration in which an endoscope is made to be movable forward and backward in an interlocking manner with forward and backward movement of the treatment tool. An endoscope insertion part 102 of an endoscope and a treatment tool insertion part 202 of a treatment tool are insertable through an overtube 300 inserted into a body wall, and a slider is provided for moving the endoscope insertion part 102 and the treatment tool insertion part 202 forward and backward in an interlocking manner. A guide part 384 that guides the endoscope insertion part 102 in a direction away from a distal end of the treatment tool insertion part 202 is provided in the vicinity of an endoscope delivery port 312 that delivers the endoscope insertion part 102 in a distal end cap 360 at the distal end of the overtube 300, and the endoscope insertion part 102 is delivered in an oblique direction from the endoscope delivery port 312.
