An image forming apparatus, comprising: a fixing part for heat-fixing an unfixed toner image formed on a recording material to the recording material, the fixing part comprising a heater that generates heat by power supplied from a commercial AC power supply; a temperature sensing element for sensing a temperature of the fixing part; a power control part for controlling the power supplied from the commercial AC power supply to the heater according to the temperature sensed by the temperature sensing element, wherein the power control part sets a power ratio according to the sensed temperature per an one-control-period, wherein the one-control period is defined as a predetermined number of continuing half-waves in an AC wave form, and the power ratio is defined as a ratio of a power actually supplied in the one-control period to the maximum power which can be supplied in the one-control period; and a current detection part provided in a power supply path from the commercial AC power supply to the heater, for detecting a current flowing in the power supply path, the current detection part ( 313; 1713; 2313; 2413) comprising a transformer ( 312; 1712) and a current detection circuit ( 313; 1713; 2313; 2413) for detecting the current via the transformer ( 312; 1712), wherein wave forms in the one-control-period corresponding to at least one power ratio among set power ratios are provided for cancelling a positive error and a negative error that are generated by the distortion of the wave form due to the transformer ( 312; 1712), the wave forms combining a phase control wave form and a wave number control wave form, wherein the wave forms include: a first group of wave forms in which power is supplied in at least a part of a negative half-wave and power is supplied in at least a part of a positive half-wave in order just after a half-wave in which no power is supplied, and a second group of wave forms in which power is supplied in at least a part of a positive half-wave just after a half-wave in which no power is supplied, or a first group of wave forms in which power is supplied in at least a part of a positive half-wave and power is supplied in at least a part of a negative half-wave in order just after a half-wave in which no power is supplied, and a second group in which power is supplied in at least a part of a negative half-wave just after a half-wave in which no power is supplied. a fixing part for heat-fixing an unfixed toner image formed on a recording material to the recording material, the fixing part comprising a heater that generates heat by power supplied from a commercial AC power supply; a temperature sensing element for sensing a temperature of the fixing part; a power control part for controlling the power supplied from the commercial AC power supply to the heater according to the temperature sensed by the temperature sensing element, wherein the power control part sets a power ratio according to the sensed temperature per an one-control-period, wherein the one-control period is defined as a predetermined number of continuing half-waves in an AC wave form, and the power ratio is defined as a ratio of a power actually supplied in the one-control period to the maximum power which can be supplied in the one-control period; and a current detection part provided in a power supply path from the commercial AC power supply to the heater, for detecting a current flowing in the power supply path, the current detection part ( 313; 1713; 2313; 2413) comprising a transformer ( 312; 1712) and a current detection circuit ( 313; 1713; 2313; 2413) for detecting the current via the transformer ( 312; 1712), wherein wave forms in the one-control-period corresponding to at least one power ratio among set power ratios are provided for cancelling a positive error and a negative error that are generated by the distortion of the wave form due to the transformer ( 312; 1712), the wave forms combining a phase control wave form and a wave number control wave form, wherein the wave forms include: a first group of wave forms in which power is supplied in at least a part of a negative half-wave and power is supplied in at least a part of a positive half-wave in order just after a half-wave in which no power is supplied, and a second group of wave forms in which power is supplied in at least a part of a positive half-wave just after a half-wave in which no power is supplied, or a first group of wave forms in which power is supplied in at least a part of a positive half-wave and power is supplied in at least a part of a negative half-wave in order just after a half-wave in which no power is supplied, and a second group in which power is supplied in at least a part of a negative half-wave just after a half-wave in which no power is supplied. a first group of wave forms in which power is supplied in at least a part of a negative half-wave and power is supplied in at least a part of a positive half-wave in order just after a half-wave in which no power is supplied, and a second group of wave forms in which power is supplied in at least a part of a positive half-wave just after a half-wave in which no power is supplied, or a first group of wave forms in which power is supplied in at least a part of a positive half-wave and power is supplied in at least a part of a negative half-wave in order just after a half-wave in which no power is supplied, and a second group in which power is supplied in at least a part of a negative half-wave just after a half-wave in which no power is supplied.