Medical system with over-tube

In a medical system including an over-tube for inserting a tool, the medical system includes a restraining mechanism for restraining at least one of a relative movement between the tool to be inserted through the over-tube and the over-tube and a relative movement between the over-tube and the body cavity. The restraining mechanism includes a mechanism for engaging the tool with the distal end of the over-tube, a mechanism for supporting the over-tube outside the body cavity, and a mechanism for connecting the endoscope to the distal end of the over-tube. When engaging the tool with the distal end of the over-tube, a resilient strip or a balloon can be used. When supporting the over-tube outside the body cavity, at least two holders can be used.