An image forming apparatus comprising: a fixing part including a heating rotation body arranged at one side of a sheet conveying path and a pressuring rotation body arranged at another side of the sheet conveying path to come into pressure contact with the heating rotation body, and being rotated at predetermined first linear velocity to sandwich and convey a sheet; a first conveying part arranged at a downstream side in a conveying direction of the sheet from the fixing part, and including a pair of rollers (35A, 35B) arranged so as to face to each other across the sheet conveying path and to come into pressure contact with each other and being rotated at second linear velocity faster than the first linear velocity to sandwich and convey the sheet; a second conveying part arranged at the downstream side in the conveying direction from the first conveying part and arranged at a side of the heating rotation body from a first reference line passing through a nip part of the fixing part and a nip part of the first conveying part, and conveying the sheet at third linear velocity faster than the first linear velocity; a biasing member biasing one roller to another roller in the pair of rollers (35A, 35B); and a separation supporting mechanism configured so as to support the one roller biased by the biasing member movably in a separating direction separating from the other roller and so as to receive force in the separating direction applied from the sheet to the one roller when the second conveying part conveys the sheet to withdraw the one roller in the separating direction from the first reference line, wherein the pressuring rotation body is made of a softer material than the heating rotation body to form the nip part dented in an inward arc shape when coming into pressure contact with the heating rotation body, the first conveying part is arranged at a side of the pressuring rotation body from a second reference line passing through both end parts (N1, N2) of the nip part of the fixing part in the conveying direction, the separation supporting mechanism is configured so as to withdraw at least the one roller to the second reference line, characterized in that the nip part of the fixing part has pressure contact force larger than pressure contact force of the nip part of the first conveying part. a fixing part including a heating rotation body arranged at one side of a sheet conveying path and a pressuring rotation body arranged at another side of the sheet conveying path to come into pressure contact with the heating rotation body, and being rotated at predetermined first linear velocity to sandwich and convey a sheet; a first conveying part arranged at a downstream side in a conveying direction of the sheet from the fixing part, and including a pair of rollers (35A, 35B) arranged so as to face to each other across the sheet conveying path and to come into pressure contact with each other and being rotated at second linear velocity faster than the first linear velocity to sandwich and convey the sheet; a second conveying part arranged at the downstream side in the conveying direction from the first conveying part and arranged at a side of the heating rotation body from a first reference line passing through a nip part of the fixing part and a nip part of the first conveying part, and conveying the sheet at third linear velocity faster than the first linear velocity; a biasing member biasing one roller to another roller in the pair of rollers (35A, 35B); and a separation supporting mechanism configured so as to support the one roller biased by the biasing member movably in a separating direction separating from the other roller and so as to receive force in the separating direction applied from the sheet to the one roller when the second conveying part conveys the sheet to withdraw the one roller in the separating direction from the first reference line, wherein the pressuring rotation body is made of a softer material than the heating rotation body to form the nip part dented in an inward arc shape when coming into pressure contact with the heating rotation body, the first conveying part is arranged at a side of the pressuring rotation body from a second reference line passing through both end parts (N1, N2) of the nip part of the fixing part in the conveying direction, the separation supporting mechanism is configured so as to withdraw at least the one roller to the second reference line, characterized in that the nip part of the fixing part has pressure contact force larger than pressure contact force of the nip part of the first conveying part.