A potentiometer comprises a cylindrical case (2) having an upper edge portion (3) and housing an electric adjustment device (5) enclosing a variable resistance, means (8) for the electrical connection of the electrical adjustment device (5) to the circuit to be controlled, a knob (9) partially inserted into the case (2), a drive shaft (10) at least partially housed in the case (2) with a first end (11) associated with the knob (9) to be integral in rotation therewith and a second end (12) interacting with the variable resistance to vary the instantaneous value thereof upon the rotation of the shaft (10). The electric adjustment device (5) comprises a box-like housing (14) coupled to the electrical connection means (8) and housing the variable resistance and having a longitudinal passing-through hole (15) suitable for snugly fit the second end (12) of the shaft (10).