To prevent the increase of a surge voltage from occurring due to multiple connection of phase control light modulation devices by shifting the off-timing of each of the phase control light modulation devices when a lot of the devices are used by connecting them to the same power source.

This device is so structured that a phase control operation is performed to semiconductor switch elements with control signals synchronized with an A.C. power source E from the outside, and thereby, light modulation is carried out by controlling the phase of the power applied to incandescent lamp loads L (L1-Ln) from the A.C. power source E. In this case, when the multiple phase control light modulation devices and incandescent lamp loads L are connected to the same power source, and the switch elements are controlled with the control signals having the same timing, a protection unit B having a current detection circuit S, a determination circuit CP and a control signal conversion circuit X2 is formed, and the off-timing of each of the phase control light modulation devices is shifted regardless of the control signal when the current flowing through the phase control light modulation device from the A.C. power source E is equal to or more than a predetermined value.