Abstract: A power-factor improvement device having a voltage stabilizer unit, a current transformer, a voltage and current comparator circuit, an operand microprocessor, a power factor driver, a voltage regulator driver, and a voltage detection circuit, wherein the voltage stabilizer unit regulates the voltage at the load; the current transformer detects the current value at the load and outputs the detected result; the voltage and current comparator circuit compares the current value outputted from the current transformer with the voltage waveform at front and rear ends of the voltage stabilizer unit and outputs a parameter data subject to the comparison result; the operand microprocessor operates the parameter data of the voltage and current comparator circuit for obtaining the best power factor value for driving the power factor driver in controlling capacitance's voltage throw-in and throw-off actions for enabling the power factor of the electric appliance at the load to be adjusted; the voltage detection circ