PURPOSE: To inexpensively provide a defect detecting circuit by providing counting for counting the number of output pulses from an error amplifier and discriminating a defect when the counted value is less than predetermined value.

CONSTITUTION: A flip-flop 12 generates one logic "1" signal at its output terminal when the one or more of the output pulses are generated from an error amplifier 5, and a flip-flop 13 generates one logic "1" signal when two or more of the output pulses are generated from the error amplifier 5. When the coil driving circuit is normal, the amplifier 5 generates more than two of the voltage pulses while the coil drive signal is logic "1". If a transistor 1 is, for example, broken down, the output of the amplifier 5 becomes one voltage pulse. Accordingly, an AND gate 15 will generate a logic "1" signal representing the defect to set the flip-flop 16 and to thus detect and store the defect. Thus, the inexpensive detecting circuit can be provided.