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. An endoscope insertion part of an endoscope and a treatment tool insertion part of a treatment tool are insertable through an overtube inserted into a body wall, and a slider is provided for moving the endoscope insertion part and the treatment tool insertion part forward and backward in an interlocking manner. A guide part that guides the endoscope insertion part in a direction away from a distal end of the treatment tool insertion part is provided in the vicinity of an endoscope delivery port in a distal end cap at the distal end of the overtube, and the endoscope insertion part is delivered in an oblique direction from the endoscope delivery port.
