A zoom camera incorporates a zoom assembly in which a zoom lens system is supported. The zoom assembly has a stationary barrel and an intermediate movable barrel. A stationary, elongated resistor element extends along the direction of movement of the zoom assembly. Nine electrodes are connected to one side of the resistor elements regularly, and grounded. Eight electrodes are connected to the opposite side of the resistor elements, and regularly alternate with the former nine electrodes. To the latter eight electrodes is applied a potential different from zero. The resistor element is divided into 16 resistor areas by the 17 electrodes. A contact brush slides on the resistor element when the movable barrel moves, and generates a voltage signal representing the contact position within each resistor area. The voltage signal is digitalized as a voltage data represented in 64 steps. A counter counts the number of times the gradient of the voltage signal changes between increase and decrease while the movable barrel moves, to designate one resistor area where the brush is located. The position of the movable barrel is identified in 1024 steps, according to the voltage data and a count signal. In a preferred embodiment, the brush is inhibited from stopping in the vicinity of positions where the electrodes are connected.