PURPOSE: To speedily start action after a line processor is initialized even in case abnormality supervisory signal is continuously inputted by detecting a change in the signal level of an input signal and generating a single pulse whose signal level changes by a previously decided time.

CONSTITUTION: If the abnormality supervisory signal er (earth potential) is inputted from an abnormality supervisory circuit to an external terminal 7, a relay 9 is energized through a diode 8 after a time t3, and a contact point 10 is operated. If a flip flop output signal (q) to be inputted changes from a high level H to a low level L at the time of t3, a monostable multivibrator 14 maintains the low level L for a prescribed time T2, and outputs a monostable multi vibrator output signal (m) and inputs it to a gate circuit 6. Consequently, the gate circuit 6 outputs a reset signal rst and inputs it to the terminal RST of the line processor 1. The line processor 1 starts action after a time t4 when the reset signal rst is set to the high level H.