To provide a positioning mechanism of a replacement blade for securely fixing the replacement blade in a reference position by preventing an error in the position of the replacement blade of a cutting tool at the time of fixing it with fastening screws.

The cutting tool is provided with a position reference part of the replacement blade on a replacement blade fitting face. An elastic body slightly longer than the thickness of the replacement blade is inserted to a through hole of the replacement blade. The fastening screw is inserted into the elastic body for screwing to the replacement blade fitting face. Before the replacement blade is fixed, the elastic body is expanded or bent by the fastening screw so that a part of the elastic body is pressed and contacted to a hole wall of the through hole on a side of the position reference part. By this pressing and contacting force, the replacement blade is pressed and contacted so as to be positioned in the position reference part.