An image heating apparatus comprising: first and second rotatable members (101, 102) forming therebetween a nip for heating a toner image on a recording material; an external heating unit including an external heating belt for externally heating said first rotatable member, first and second supporting rollers (103, 104) for rotatably supporting said external heating belt at an inner surface thereof and for urging said external heating belt toward said first rotatable member, an urging member (301R, 301L) for urging said first supporting roller in a direction away from said second supporting roller, a holding mechanism for rotatably holding said first and second supporting rollers (103, 104) and for permitting relative movement of said first supporting roller relative to said second supporting roller, and a temperature detecting element, opposed to said first supporting roller through said external heating belt between itself and said first supporting roller, for detecting a temperature of said external heating belt by contacting with an outer surface of said external heating belt; and a moving mechanism for moving said external heating unit between a first position in which said external heating belt contacts said first rotatable member and a second position in which said external heating belt is away from said first rotatable member, characterized in that said temperature detecting element is disposed such that in a state that a temperature of said external heating belt is maintained at a predetermined temperature, a detected temperature at a predetermined position between the first position and the second position is higher than detected temperatures at the first position and the second position. first and second rotatable members (101, 102) forming therebetween a nip for heating a toner image on a recording material; an external heating unit including an external heating belt for externally heating said first rotatable member, first and second supporting rollers (103, 104) for rotatably supporting said external heating belt at an inner surface thereof and for urging said external heating belt toward said first rotatable member, an urging member (301R, 301L) for urging said first supporting roller in a direction away from said second supporting roller, a holding mechanism for rotatably holding said first and second supporting rollers (103, 104) and for permitting relative movement of said first supporting roller relative to said second supporting roller, and a temperature detecting element, opposed to said first supporting roller through said external heating belt between itself and said first supporting roller, for detecting a temperature of said external heating belt by contacting with an outer surface of said external heating belt; and a moving mechanism for moving said external heating unit between a first position in which said external heating belt contacts said first rotatable member and a second position in which said external heating belt is away from said first rotatable member, characterized in that said temperature detecting element is disposed such that in a state that a temperature of said external heating belt is maintained at a predetermined temperature, a detected temperature at a predetermined position between the first position and the second position is higher than detected temperatures at the first position and the second position.