Safety device for on/off switch of an electric tool

A safety device for an on/off switch of electric tool, comprising:

• a casing having a switch;
• a knob pivotally jointed to said casing;
• a first link lever having a first slot at one end and a second slot at a position adjacent to the midpoint thereof;
• a second link lever having its midpoint pivotally jointed to said casing and one end pivotally jointed to one end of said first link lever while the other to said knob;
• a trigger having one end pivotally jointed to said casing while the other to the first slot of said first link lever;
• and
• a dog having one end pivotally jointed to the second slot of said first link lever while the other is provided with a protruding portion at a position corresponding to said switch;
• whereby, in operation of an electric tool of this kind, a user is requested to depress both said trigger and knob with his two hands respectively and simultaneously so that the dog is pulled upwardly to travel a longer-distance stroke to have its protruding portion depressed the switch, otherwise, by depressing either said trigger or knob with a single hand, the operation is in vain.