PURPOSE: To carry out ON/OFF of load without altering an apparatus for controlling load by supplying electric power to the load for a period during one zero cross point to the next zero cross point in the case that the level of an input signal is in one level against a difference level and shutting electric power supplied to the load in the case that the level is another level.

CONSTITUTION: An input signal is level-discriminated by previously set difference level through a level discriminating circuit 11 at a prescribed time prior to the zero cross point of a.c. electric power source 1. When the level of an input signal is one level as compared with a prescribed discrimination level, electric power is supplied to load from the a.c. electric power source 1 during from the period of said zero cross point to next zero cross point. When the level of said input signal is another level as compared with the discrimination level, electric power source supply from the a.c. power source is stopped during a period from a zero cross point to next zero cross point.