A heater controller performs on/off control of a plurality of heaters and includes a storage unit that stores therein a plurality of pattern sets. Each of the pattern sets includes a plurality of heater-on/off patterns for respectively controlling the heaters. The heater controller calculates a reference value representing an average of values of electric power supplied to the heater controller over a predetermined period of time; calculates, for each of the pattern sets, an output power value to be supplied to the heaters when the heaters are turned-on according to the heater-on/off patterns included in the pattern set; calculates, for each of the pattern sets, a difference between the reference value and the output power value; selects, from the pattern sets, one pattern set having a smallest difference; and performs on/off control of the heaters according to the heater-on/off patterns included in the pattern set thus selected.