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 inside the overtube body that guides an endoscope and a treatment tool into a body cavity, the first valve member provided in the endoscope insertion passage, and the second valve member provided in the treatment tool insertion passage. F1>F3 and F2>F3 are satisfied when a fixing force for fixing the slider to the endoscope is defined as F1, a fixing force for fixing the slider to the treatment tool is defined as F2, and a frictional force that receives from the first valve member when the endoscope moves forward and backward is defined as F3.