The image forming apparatus has a heat member for heating an unfixed image and is configured so that a longitudinal center of the heat member becomes a conveyance center of the recording material, the image forming apparatus including a central portion temperature detection part adjacent to the conveyance center, an end portion temperature detection part for detecting an end portion temperature of the heat member, and a width detection part for detecting a lateral width of the recording material, wherein the width detection part is disposed at a side opposite to a side at which the end portion temperature detection part is disposed with respect to the conveyance center position of the recording material. The image forming apparatus achieves the control for error setting of the recording material based on the width detection part and the end portion temperature detection part.