Abstract: A well casing perforator adapted to be used with pneumatically powered rotary drilling equipment. It includes an upright elongated body which is inserted within the casing. The body is attached to the lower end of a drill rod which imparts vertical or angular movement to the elongated body while within the casing. The body is guided axially within the casing by rollers which engage the interior casing wall. A rotatable wheel has teeth capable of penetrating the casing wall as the wheel rolls in engagement with the casing. The wheel is mounted at the outer end of a carrier pivoted to the elongated body about a horizontal axis. The carrier in turn is controlled by a piston assembly subject to pneumatic pressure within the drill rod. The piston assembly is pivotally connected to the carrier to move it from a first position at which the wheel is retracted from engagement with the casing to a second position at which the wheel engages the interior wall of the casing.