DETECTOR FOR DEFECT IN SWITCHING ELEMENT

PROBLEM TO BE SOLVED: To provide a detector for defect in switching elements for use in the control circuit of a battery forklift or the like which detector makes it possible to reduce the cost of the detector without increase in the size of the control circuit on a CPU board or the like, especially. SOLUTION: Using a motor drive circuit 13 for driving a PS motor 16 for steering control, for example, the PS motor 16 is driven by drive-controlling transistors Q5-Q8. Welding in MPS 12 for turning on/off power supply from a battery 11 to the motor drive circuit 13 and short circuits in transistors Q5 and Q7 are detected using a single voltage input I/F 17 and a drive control circuit 15. If a battery voltage VB is outputted to a wiring position P3 when the MPS 12 is turned off to turn on the transistors Q5 and Q7, for example, it is judged that the MPS 12 is defective. If a battery voltage VB is outputted to the wiring position P3 when the MPS 12 is turned on to turn off the transistors Q5 and Q7, for example, it is judged that the transistor Q5 or Q7 is defective.