The present invention provides a safety locking device for harrows of a tractor. The safety locking device comprises: a connecting frame (10) which is provided on one side of a rotavator (B) or a mounted unit (C) in a vertically rotatable manner； a central harrow blade (20) which is mounted on the front of the connecting frame (10)； a pair of outer harrow blades (30) which are provided to be able to fold or spread on both sides of the central harrow blade (20)； a cylinder (40) which is mounted on one side above the rotavator (B) or the mounted unit (C) so as to vertically rotate the central harrow blade (20)； and a safety locking unit (100). While the central harrow blade (20) is rotated downwardly due to a forward operation of the cylinder (40), the safety locking unit (100) maintains a locked state so as to prevent the outer harrow blades (30) from spreading horizontally, and while the central harrow blade (20) is rotated upwardly due to a backward operation of the cylinder (40), the safety locking unit (100) releases the locked state, allowing the outer harrow blades (30) to spread horizontally. The present invention can prevent pre-emptively safety accidents where due to an operator&prime；s mal-operation or malfunction of the cylinder, the outer harrow blades accidentally unfold, hitting operators in the vicinity. In addition, the present invention can prevent crashes that may occur against structures nearby, ridges between rice paddies, or the like, as the outer harrow blades abruptly unfold, and thus can increase durability and service life.COPYRIGHT KIPO 2020본 발명은 로터베이터(B) 또는 장착유닛(C)의 일측에 상하로 회동할 수 있도록 형성하는 연결프레임(10)； 상기 연결프레임(10)의 전방에 장착하는 중앙 써레날(20)； 상기 중앙 써레날(20)의 양측에 접거나 펼쳐지도록 형성하는 한 쌍의 외측 써레날(30)； 로터베이터(B) 또는 장착유닛(C)의 상부 일측에 상기 중앙 써레날(20)을 상하로 회동시킬 수 있도록 장착하는 실린더(40)； 상기 실린더(40)의 전진 작동으로 상기 중앙 써레날(20)이 하부로 회동한 상태에서 상기 외측 써레날(30)이 수평으로 펼쳐지지 않도록 잠금 상태를 유지하고 상기 실린더(40)의 후진 작동으로 상기 중앙 써레날(20)이 상부로 회동한 상태에서 상기 외측 써레날(30)이 수평으로 펼쳐질 수 있도록 잠금 상태를 해제하는 안전 잠금유닛(10
