The trigger safety mechanism is a pivoted element (102) in which lower part there is a shaped fork (103) through of which linear guide (106) there is a guidance means (104); in which upper part there is an articulated transmission rod (101) that is supported by its other end on the hammer, being a separation space (100) between the hammer (6) and the operation end of the valve (12a) when the trigger (5) is in resting position; and in a point of the surface of the pivoted element (102) there is a rotation axis (107); so that when the trigger is moved to an active position, the guidance means passes through the interior of the linear guide so that the said pivoted element drags the rod, allowing the hammer (6) to impact the valve.