To prevent excessive temperature rise and fire of an IC.

In a breaker mechanism 120, the left end part of metal plates 121, 122 having mutually different thermal expansion coefficient is fixed by solder to a contact 124 of wiring 55 for driving VDD 2 connected to a drive pulse power supply, and the right end part is fixed to wiring 55a connected to a driver IC by a low melting point solder 132. When the temperature of the driver IC is lower than a prescribed temperature, the wiring 55a and the wiring 55b are conducted through the metal plate 121, 122. On the other hand, when the temperature of the driver IC becomes the prescribed temperature or more, the low melting point solder 132 is melted by the heat transmitted from the driver IC through the wiring 55a, and the metal plates 121, 122 are deformed so that the portion fixed to a contact 123 may be separated from the substrate 65 due to the mutual difference of the thermal expansion coefficient and connection of the wiring 55a and the wiring 55b is cut off.