PURPOSE: To reduce the consumption of a battery by turning off a switch circuit when a resistance variation factor does not operate.
CONSTITUTION: A tactile sensor 1 and a 2nd resistance body 2' are connected in series and a 1st resistance body connected in parallel to the tactile sensor 1 constitutes a detecting circuit by interposing a switch 5. A voltage comparator formed by connecting resistance bodies 6 and 7 in series is provided in parallel to the series circuit of the tactile sensor 1 and 2nd resistance body 2 and a comparator 8 which compares their divided voltages with each other is connected to constitute a bridge circuit. The switch 5 is driven with a signal outputted by the comparator 8. The comparator 8 operates only when a pressing force is applied to the tactile sensor 1 and the resistance 4 is connected in parallel to the tactile sensor 1.