According to the present invention, it is possible to allow an insertion part of an endoscope inserted into an outer tube and an insertion part of a treatment tool to move back and forth in interlock with each other, as well as possible to reliably prevent an operation part of the treatment tool from interfering with a proximal end of the endoscope at the time of operation of inserting the treatment tool into the outer tube. An endoscopic surgery device 1 of the present invention satisfies the following expressions: Lt ‰¤ Ls <； Lh, and Lh ‰¥ Ls1 + Ls + t, where Lt is a length of the outer tube, Ls is a length of a hard part of the insertion part of the endoscope, Lh is a length of a hard part of the insertion part of the treatment tool, Ls1 is a minimum projection length of a distal end of the insertion part of the treatment tool with respect to a distal end of the insertion part of the endoscope, and t is an allowance amount.
