A SAFETY CUTTER KNIFE

A safety cutter knife is provided to safely perform a cutting work by restraining the protrusion length of a blade with a connecting unit formed in a protection device and limiting right and left movement of the blade with a blade groove formed in a support. A safety cutter knife includes a case(200), a blade(100), a sliding member(300), and a protection device(400). The case is configured to make a user readily grip the case. The blade is accommodated in the case to be reciprocally moved. The sliding member is fastened to the blade to adjust reciprocal movement of the blade. The protection device is installed at one side of the case to prevent damage of an object by the blade. The protection device is detachably installed at a tip of the case by a fastening unit. The protection device includes a front cap(420), and a support unit. The front cap is coupled to the front end of the case to guide extraction of the blade. The support unit is formed at one side of the front end of the front cap to help to cut an object with the blade.