An electric power unit for driving a matrix-type display unit in alternating cycle mode has a multiplicity of buffer circuits for generating a multiplicity of high output voltages (high output voltage group) and a multiplicity of buffer circuits for generating a multiplicity of low output voltages (low output voltage group). A power supply voltage is stepped up by a first and a third voltage conversion circuits into a first and a third output supply voltages. The highest voltage of the high output voltage group is stepped down by a second voltage conversion circuit to output a predetermined second output power supply voltage. These first through third output power supply voltages are used as the operating voltages of the buffer circuits. Also, the power supply voltage is stepped up by the second voltage conversion circuit to generate the second output power supply voltage, which voltage is further stepped up by the first voltage conversion circuit to generate the first output power supply voltage.