A cutting unit for a slot-type perforator is mounted in a casing having a specific edge, driven by a piston or plunger. The cutting unit includes cutting tools associated with a first holder immovable relative to the piston, and a second holder, including a recess, cooperating with the casing's edge, immovable relative to the casing. The holders move relative to each other causing extending and retracting the cutting tools in opposite directions, during piston's movements. The cutting unit includes a retractable mechanism to bring its parts into a transportation position and to fix them therein. The retractable mechanism includes a guide groove made in the second holder, and a connecting rod attached to the first holder. The rod moves through the groove ensuring the return of the second holder into the transportation position, wherein it is fixed absent pressure upon the piston, caused by interaction of the edge and recess.