A retractable universal safety scalpel comprising a handle having a proximal section and a distal section with a longitudinally extending bore defining a housing； a blade carrier element having mid-section, proximal end and a distal end on which is secured a blade slidably mounted within said housing being capable of getting exposed from the end of distal section； first and second slider elements secured to said blade carrier element through a recess formed in the said handle extending from the forward end closer to the said opening to the rear end closer to the distal section in a slidable arrangement with the said housing and extending externally in an axial direction of said housing to move said blade carrier moving the said blade from an un-exposed pre-use position to an exposed in-use position and to an after-use position capable of covering and locking permanently the said blade member completely within the said housing of the said handle； a plurality of locking means is provided in the said housing to enable locking of the blade in an un-exposed pre-use position to an exposed in-use position and to an after-use position capable of covering and locking permanently the said blade member wherein the said housing being provided with lock cooperating mechanisms at three positions thereon corresponding to pre-use, in-use and post-use disposal stages, said lock cooperating mechanisms cooperating with the respective locking means provided thereon.一種可伸縮安全手術刀包含一把手、一刀片承載件、第一滑動件與第二滑動件以及複數鎖定手段。把手具有一靠近端與一遠離端。把手具有一縱向延伸開孔，而定義出一外殼。刀片承載件具有一中段、一靠近端以及一遠離端。一刀片係固設於所述刀片承載件上，且所述刀片係可滑動地設置於外殼內並且可以自外殼之遠離端露出。第一滑動件與第二滑動件係藉由形成於把手內之一凹入部而固設於所述刀片承載件，並且自把手之較靠近外殼之開口的前端朝向較靠近把手之遠離端的後端延伸，並可滑動地設置於外殼且沿所述外殼之軸方向延伸而可將刀片自一欲使用未露出狀態移動至一使用中露出狀態以及一使用後狀態，於使用後狀態係可以完全地將該刀片永久地覆蓋與鎖固於把手之外殼內。複數鎖定手段係設置於外殼內而可以將刀片自欲使用未露出狀態移動至使用中露出狀態以及使用後狀態，於使用後狀態係可以完全地將刀片永久地覆蓋與鎖固於把手之外殼內。其中，外殼於三處位置具有一鎖固協同機構而分別對應欲使用狀態、使用中狀態以及使用後狀態，鎖固協同機構係對應前述複數鎖定手段。
