PURPOSE: To provide an electric safety system for controlling the insertion of an absorbing rod into the core of a reactor to a trip signal.

CONSTITUTION: Switches 8 and 9 and 100 and 104 formed of two groups are connected between a power source 10 and a rod magnet 1. The switches 8, 9 of one group are controlled by signal converters 54, 79 and 81 receiving input signals from different guard lines A, B. The other switch group 100 and 104 is also controlled by the links 120-131 and 108-119 of an optisolator/photo detector for receiving the input signal from the guard lines. When the obstruction of a reactor is detected by a plurality of sensors of the group of obstruction sensors, supply of input signal to the signal converters and optical links is interrupted, and the switches are opened, whereby the supply of power to the magnet is interrupted.