Provided are an endoscopic surgical device and an overtube that allow the state of a distal end of a treatment tool to be easily checked while achieving a decrease in 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 the forward and backward movement of a treatment tool. An overtube 300 to be inserted into a body wall is provided with an endoscope insertion passage 306 through which the endoscope is inserted and a treatment tool insertion passage 308 through the treatment tool is inserted, the treatment tool insertion passage 308 is provided parallel to a reference axis 300a of the overtube 300, and the endoscope insertion passage 306 is provided obliquely to the reference axis 300a. A slider, which is engaged with the endoscope and the treatment tool inserted through the respective insertion passages and causes the endoscope and the treatment tool to interlock with each other and move forward and backward, is arranged inside the overtube 300 so as to be movable in a forward-backward direction of the overtube 300. An endoscope engagement part engaged with the endoscope in the slider is movable in an upward-downward direction, and moves upward and downward along the position of the oblique endoscope insertion passage 306 together with the movement of the slider in the forward-backward direction.
