A safety electric switch, comprising a casing (2,3,4) with at least two slots (18, 19) for the insertion of a key actuator (20) of pre-defined shape, at least one pair of electric contacts (5,5', 6,6',7,7',8,8') disposed in the casing (3) and displaceable between a closed and an open position, a cam (15) mounted inside the casing (4) and operatively connected to the contacts to promote their movement and commutation, the cam being rotatable around a first axis (H) by insertion of the actuator in the casing, blocking means (22) adapted to prevent rotation of the cam (15) and the consequent displacement of the contacts, elastic means (23) acting on the blocking means (22) to maintain them in a cam blocking position when the actuator is disinserted from the casing. The blocking means (22) comprise at least one lever element (24,24') pivoted about a second axis (K) distal from the first axis (H) and positioned so as to act on one side face of the cam (15). The second pivot axis (K) is substantially parallel to the cam pivot axis (H).