PURPOSE: To obtain a static electricity sensor which has a high sensitivity and also is operated by a low voltage, by using transistors of an optional number of ≥3 pieces, and the current amplifying operation of said transistors.

CONSTITUTION: The base of a transistor TRT1 of the first stage, and the base of the next stage and thereafter are connected to an external terminal 1 and the emitter of the previous stage, respectively. Also, the collector of each stage is connected to an external terminal 2, and the collector of the final stage and the emitter are connected to an external terminal 3 and an external terminal 4, respectively. In this regard, the circuit is shielded by a metallic plate 5. In this state, when the + pole of static electricity approaches a detecting metallic rod 6, the static electricity is discharged to the base and the emitter of the TRs T1 through T6 from the rod 6, and a current flows to a battery 9 through the battery 9, a resistance 7, the collector and the emitter of the TRT1, and the base and the emitter of the TRs T2 through T6. This current increases a current between the collector and the emitter of the TRT2 and flows to the base and the emitter of the next stage and thereafter. In such a way, the current amplifying operation is repeated, and the amplifying current flows between the base and the emitter of the TRT6, by which the detecting current flows in a loop through the battery 9, an ammeter 8, the collector and the emitter of the TRT6, and the battery 9, and static electricity is detected.