PURPOSE: To enable the open condition of a movable terminal to be surely detected, by constituting a device, in which voltage higher than the reference voltage applied to a throttle sensor or the like is applied to an A/D converter through a pull-up resistor, and obtaining a margin in the amount of a voltage effect by the pull-up resistor.

CONSTITUTION: Reference voltage Vcc is applied to fixed terminals 1a, 1b in both ends of the potentiometer-type throttle sensor 1, and its movable terminal 1c is connected with interlocking to a throttle valve. The movable terminal 2c is connected to the ground through a resistor R1 and a capacitor C1 in series, and their connection point is connected with a detection voltage input terminal I of an A/D converter 2. While reverse current preventing diodes D1, D are provided. In this case, a pull-up resistor Ro' is connected between the output terminal of a power source, outputting voltage VB higher than the reference voltage Vcc, and the movable terminal 1c. In this way, an open condition of the movable terminal 1c can be surely detected by obtaining a margin of V-Vcc as compared with those in the past.