A power limiting circuit for controlling the power of the incandescent lamp not to overrun the rated power limit includes a sampling circuit that consists of two resistors connected in parallel. A control chip compares the received sample voltage with the standard voltage then outputs control signal to drive the conduction of a SCR (silicon controlled rectifier) to change the inner states of contacts of a relay so as to further control the on/off between the input and the output. Based on this control process and technique, this invention prevents the employment of incandescent lamps having a greater power than power rating. Besides, a bi-operational amplifier circuit is used to fulfill the whole examination and control perfectly.