A high-side driver has a semiconductor element being connected in series in a power supply path extending from a DC power source to a linear solenoid and turned on/off to control a current of the linear solenoid. The high-side driver includes a current detector of a current of the linear solenoid, a controller of the semiconductor element, a state detector of the high-side driver or the linear solenoid and output a state signal, a first transmit buffer to latch and output the state signal, a second transmit buffer to output the state signal without latching the same, and a transmit shift register to convert the state signal into serial data and transmit the serial data to an external device at predetermined timing. The state detector selects at least one of the first and second transmit buffers and outputs the state signal to the selected one.