Provided is an endoscopic surgical device and an overtube with which a surgeon can easily obtain a desired image and operability is high. The overtube includes a slider within an overtube body, which guides an endoscope and a treatment tool into a body cavity. An endoscope-coupled part and a treatment tool-coupled part are provided inside the slider, and the slider has a dead zone where the forward and backward movement of either the endoscope or the treatment tool does not interlock with the movement of the other and a sensing zone where the forward and backward movement of either the endoscope or the treatment tool interlocks with the movement of the other. F1>F2 is satisfied when a fixing force for fixing the endoscope-coupled part to the endoscope tool is defined as F1 and a fixing force for fixing the treatment tool-coupled part to the treatment tool is defined as F2.