An image forming apparatus, comprising: an image forming mechanism configured to form a toner image on a recording sheet; and an image fixing unit configured to fix the toner image onto the recording sheet, the unit comprising: a magnetic flux generator configured to generate a magnetic flux; a heat member (22, 23) configured to be heated inductively by the magnetic flux generated by the magnetic flux generator; a magnetic flux adjuster configured to reduce the magnetic flux active on the heat member (22, 23) to form a heat reduction area in an outer circumferential surface of the heat member (22, 23) in a width direction thereof; a controlling member configured to move the magnetic flux adjuster to change the heat reduction area based on a width (L1, L2) of the recording sheet when a toner image fixing process is started; and a first temperature detector arranged at a position where the first temperature detector is maintained outside the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster, wherein the temperature detector is configured to detect a temperature of the heat member (22, 23), characterized in that the controlling member is further configured to move the magnetic flux adjuster to change the heat reduction area in accordance with a temperature detected by the temperature detector and in that a second temperature detector is arranged at a position such that the second temperature detector is maintained within the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster. an image forming mechanism configured to form a toner image on a recording sheet; and an image fixing unit configured to fix the toner image onto the recording sheet, the unit comprising: a magnetic flux generator configured to generate a magnetic flux; a heat member (22, 23) configured to be heated inductively by the magnetic flux generated by the magnetic flux generator; a magnetic flux adjuster configured to reduce the magnetic flux active on the heat member (22, 23) to form a heat reduction area in an outer circumferential surface of the heat member (22, 23) in a width direction thereof; a controlling member configured to move the magnetic flux adjuster to change the heat reduction area based on a width (L1, L2) of the recording sheet when a toner image fixing process is started; and a first temperature detector arranged at a position where the first temperature detector is maintained outside the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster, wherein the temperature detector is configured to detect a temperature of the heat member (22, 23), characterized in that the controlling member is further configured to move the magnetic flux adjuster to change the heat reduction area in accordance with a temperature detected by the temperature detector and in that a second temperature detector is arranged at a position such that the second temperature detector is maintained within the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster. a magnetic flux generator configured to generate a magnetic flux; a heat member (22, 23) configured to be heated inductively by the magnetic flux generated by the magnetic flux generator; a magnetic flux adjuster configured to reduce the magnetic flux active on the heat member (22, 23) to form a heat reduction area in an outer circumferential surface of the heat member (22, 23) in a width direction thereof; a controlling member configured to move the magnetic flux adjuster to change the heat reduction area based on a width (L1, L2) of the recording sheet when a toner image fixing process is started; and a first temperature detector arranged at a position where the first temperature detector is maintained outside the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster, wherein the temperature detector is configured to detect a temperature of the heat member (22, 23), characterized in that the controlling member is further configured to move the magnetic flux adjuster to change the heat reduction area in accordance with a temperature detected by the temperature detector and in that a second temperature detector is arranged at a position such that the second temperature detector is maintained within the heat reduction area, regardless of how the controlling member changes the heat reduction area by moving the magnetic flux adjuster.