An automatic exposure control apparatus of electric type for a photographic camera having an exposure control parameter setting means cooperative with a geometrical progression scale in isometric graduation is provided with a resistor device. The device includes a variable resistor having a grounded slider associated with the setting means upon movement thereof for providing a resistor value proportional to the amount of movement of the setting means, but to the reciprocal logarithm of the preselected parameter value. In order to minimize the complexity of a computer circuit responsive to the various outputs of the resistor device for performing photographic Appex computation, a bias voltage is applied to each of the variable resistors in a manner to produce a signal in the form of current proportional to the reciprocal of the amount of movement of the setting means. The resistor device has a single substrate having a plurality of resistor elements formed thereon by a metal coating technique and arranged for cooperation with respective sliders, thereby improving the exposure control accuracy and stabilization of the performance of the computer circuit against variation of temperature distribution in the apparatus.