PURPOSE: To disturb a mechanical vibration and to place a piezoelectric ceramic transformer on various type electric circuits without deteriorating characteristics by fixedly supporting a node part of the vibration of the transformer at the time of placing the transformer on the circuits.

CONSTITUTION: A case to be used to mount a printed board or the like on an electric circuit is formed of an upper case 1 formed of heat resistant resin and a lower case 2 in which metal lead terminal 3 is implanted for connecting the board. Supporting protrusions 4a, 4b for a piezoelectric ceramic transformer 6 and a protrusion 5 for preventing drop are provided at inner four corners of the cases 1, 2, and the protrusions 4a, 4b are provided at positions for supporting the node part of a mechanical vibration of the transformer 6. The transformer 6 is fixed in the case by suppressing the node parts of the vibrations of the four corners by the protrusions 4a, 4b.