A miniaturizable, low-cost highly reliable inverter unit. A control circuit section for controlling operating timing of high breakdown voltage semiconductor elements included in an inverter circuit section and first and second drive and abnormality detection circuit sections for outputting drive signals for driving the high breakdown voltage semiconductor elements according to the operating timing and for feeding back an abnormality of the inverter circuit section to the control circuit section are formed on an SOI substrate as one integrated circuit chip. On the integrated circuit chip, circuit formation areas which differ in reference potential are separated from one another by dielectrics. A plurality of level shifters for transmitting signals exchanged between circuit formation areas separated by the dielectrics are formed.