An endoscope and a treatment tool which are inserted into an outer tube can move back and forth in interlock with each other, and an operation part of the treatment tool can be prevented from interfering with a proximal end of the endoscope when inserting the treatment tool into the outer tube. An endoscopic surgery device 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.
