An image forming apparatus, comprising: a fixing portion that is configured to heat-fix an unfixed toner image formed on a recording material onto the recording material, the fixing portion comprising: an endless belt; and a heater that is configured to contact an inner surface of the endless belt and to generate heat by power supplied from a commercial alternative current power source; a temperature detection element (18, 19) that is configured to detect a temperature of said fixing portion; and a power control portion that is configured to control the power supplied from the commercial alternative current power source to the heater according to the temperature detected by the temperature detection element (18, 19), wherein the power control portion is capable of setting: a first power supply control mode, with a predetermined number of half waves more than two continuous waves in an alternative current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; a second power supply control mode, with a predetermined number of half waves equal to or less than the two continuous waves in the alternative current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; and a third power supply control mode for supplying predetermined power to the heater, wherein the power control portion is configured to switch, before a leading edge of the recording material enters the fixing portion, a state of supplying the power in the first power supply control mode to a state of supplying the power in the second power supply control mode, then to switch the state of supplying the power in the second power supply control mode to a state of supplying the power in the third power supply control mode, and to further switch the state of supplying the power in the third power supply control mode to the state of supplying the power in the first power supply control mode, wherein the power control portion is configured to issue a switching of the state of supplying the power in the first power supply control mode to the state of supplying the power in the second power supply control mode at a timing at least one control cycle of the first power supply control mode prior to a timing of switching the state of supplying the power in the second power supply control mode to the state of supplying the power in the third power supply control mode, and wherein the fixing portion is configured to fix the unfixed toner image onto the recording material in the state of supplying the power to the heater in the first power supply control mode. a fixing portion that is configured to heat-fix an unfixed toner image formed on a recording material onto the recording material, the fixing portion comprising: an endless belt; and a heater that is configured to contact an inner surface of the endless belt and to generate heat by power supplied from a commercial alternative current power source; an endless belt; and a heater that is configured to contact an inner surface of the endless belt and to generate heat by power supplied from a commercial alternative current power source; a temperature detection element (18, 19) that is configured to detect a temperature of said fixing portion; and a power control portion that is configured to control the power supplied from the commercial alternative current power source to the heater according to the temperature detected by the temperature detection element (18, 19), wherein the power control portion is capable of setting: a first power supply control mode, with a predetermined number of half waves more than two continuous waves in an alternative current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; a second power supply control mode, with a predetermined number of half waves equal to or less than the two continuous waves in the alternative current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; and a third power supply control mode for supplying predetermined power to the heater, wherein the power control portion is configured to switch, before a leading edge of the recording material enters the fixing portion, a state of supplying the power in the first power supply control mode to a state of supplying the power in the second power supply control mode, then to switch the state of supplying the power in the second power supply control mode to a state of supplying the power in the third power supply control mode, and to further switch the state of supplying the power in the third power supply control mode to the state of supplying the power in the first power supply control mode, wherein the power control portion is configured to issue a switching of the state of supplying the power in the first power supply control mode to the state of supplying the power in the second power supply control mode at a timing at least one control cycle of the first power supply control mode prior to a timing of switching the state of supplying the power in the second power supply control mode to the state of supplying the power in the third power supply control mode, and wherein the fixing portion is configured to fix the unfixed toner image onto the recording material in the state of supplying the power to the heater in the first power supply control mode.