PURPOSE: To contrive to save the space by unnecessitating light emitting diodes installed externally by a method wherein a MOS IC substrate is partly provided with an MOSFET which starts its action at the maximum voltage of the MOSIC.

CONSTITUTION: The FET12 is formed on the LSI circuit substrate 11. Further, a protection resistor R is formed as required. The FET is an MOSFET having VTH set at 1.6∼1.7V, and does not turn on while the impressed voltage of the circuit is lower than the standard voltage 1.5V of solar batteries. Therefore, there is no variation in the voltage and no consumed current. On the other hand, it begins to turn on when the voltage reaches over 1.6∼1.7V; accordingly, current flows, thus allowing no A point voltage to exceed a preset voltage.