A backlash vibration mechanism (a) used in a toy gun and arranged above a piston-cylinder mechanism (b) is disclosed, having a weight (2) inserted through a disarm mechanism (g), a reaction spring (3) adapted for returning the weight (2) after the weight (2) having been moved backwards and a brake unit (4) arranged at the front side relative to the disarm mechanism (g) and adapted for pushing the disarm mechanism (g) backwards to simulate the action of the disarm mechanism (g) of a real gun when producing a backlash vibration.