The invention directed to a portable handheld drilling apparatus for receiving and driving a drill which can encounter a drilling resistance during a drilling operation thereby causing the drilling apparatus to undergo an unwanted rotational movement. The drilling apparatus of the invention includes: a handle for holding by an operator while performing the drilling operation; a drive motor; a transmission for driving the drill; a centrifugal clutch assembly mounted between the drive motor and the transmission; a brake device movable between an inactive position and a braking position; a trigger lever movable between a first position wherein the trigger lever is at rest and a second position; the trigger lever being operatively connected to the brake device so as to trip the brake device into the braking position when the trigger lever moves from the first position into the second position; and, an actuating device for acting upon the trigger lever to cause the trigger lever to move into the second position when the unwanted rotational movement exceeds a pregiven limit value.