The present invention relates to a caulking gun apparatus comprising an elongate housing (1) for holding a cartridge (6) in a dispensing position, a piston rod (2) for engaging the cartridge for dispensing the caulking material and at least one driving lever (3) in slideable engagement with the piston rod. The apparatus further comprises a motor (4) means which is disposed within the elongate housing and coupled to a motor shaft (4') and a transmission mechanism such that during rotation of the rotary motor shaft, power is transmitted from the rotary motor to the piston rod. The apparatus further comprises a mechanical mechanism (7) for operating the piston rod when the rotary motor is disabled.