A power control method includes heating a heating roller provided to fix a toner image of print data in an image forming apparatus, the heating roller having a heating resistor to receive roller power. The power control method includes gradually increasing a maximum level of a source power supplied from an external source up to a specific maximum supply level, supplying the maximum source power to the heating resistor as the roller power while gradually increasing the maximum level of the source power up to a specific maximum supply level, measuring a surface temperature of the heating roller, further supplying the source power of which maximum level is equal to the maximum supply level to the heating resistor as the roller power until the measured surface temperature reaches a specific fixing target temperature, and fixing the toner image onto a fed printing medium.