In a drive unit for use with a matrix type display, a buffer circuit of the power supply circuit of the drive unit has an high-voltage first output circuit and a low-voltage second output circuit for generating the same output voltage under a normal operating condition, wherein the high-voltage output circuit has enhanced capability of providing output current to bring up the output voltage and the low-voltage output circuit has enhanced capability of providing output current to bring down the output voltage. A voltage detected at a node connected to the output end of the buffer circuit is compared with a bias voltage. Based on the comparison, the outputs of the first and second output circuits are switched over from one to the other as it is supplied to the display.