A device is provided for releasing a spear shaft of a spear gun for scuba diving or the like. The shaft has a latch element formed on a first lever pivotally connected at its front end to a screw attached to and integrally with a frame of the gun, the lever being maintained elastically in a resting position. The gun has a trigger with an abutment portion forced elastically against the front end of the first lever extending forward of a convex upper surface. The convex upper surface intersects a concave surface at an edge that traces a first circular trajectory when the trigger is rotated. A second lever is rotatably connected to the frame, the front end of the second lever being movable along a second circular trajectory intersecting the first circular trajectory. An arm of the second lever extends so as to intersect the trajectory of the spear shaft when it is loaded in the gun, such that the shaft abuts the latch element first, thereby moving the first lever away from its resting position, until it engages a shaped cavity of the shaft, and subsequently abuts the arm of the second lever. This causes the second lever to turn until it abuts the first lever in line with the latch element, simultaneously raising its front end up to and against the convex surface of the trigger. The front end of the first lever is slidingly connected to a screw, such that the first lever may be variably displaced, thereby adjusting the force applied by the second lever to the trigger.