A fixing device, comprising: a roller; an endless belt having a portion facing the roller; and a heating member disposed such that the portion of the endless belt is between the heating member and the roller, the heating member extending in a width direction of the endless belt and pressing the portion of the endless belt against the roller such that a sheet can be passed in a sheet conveying direction through a nip formed between the roller and the portion of the endless belt and an image on the sheet can be fixed thereto, wherein the heating member includes a first heat generating member group, a second heat generating member group and a third heat generating member group that are disposed along the width direction, and the first heat generating member group is independently operable from the second and third heat generating member groups, wherein the fixing device further comprises a switching unit of electric conduction with respect to each heat generating member groups (361-1, 361-2, 361-3), the first heat generating member group is provided at a center in the width direction, the second heat generating member group is arranged on an outside of the first heat generating member group in the width direction and the third heat generating member group is arranged on an outside of the second heat generating member group in the width direction, heat generating members of the second heat generating member group are arranged symmetrically on both outer sides of the first heat generating member group in the width direction, and heat generating members of the third heat generating member group are arranged symmetrically on both outer sides of the first heat generating member group in the width direction; characterized in that a pair of heat generating members of the second heat generating member group arranged symmetrically on both outer sides of the first heat generating member group are connected in series, a pair of heat generating members of the third heat generating member group arranged symmetrically on both outer sides of the first heat generating member group are connected in series, and each pair is individually controlled by the switching unit having a plurality of switching elements corresponding to each pair. a roller; an endless belt having a portion facing the roller; and a heating member disposed such that the portion of the endless belt is between the heating member and the roller, the heating member extending in a width direction of the endless belt and pressing the portion of the endless belt against the roller such that a sheet can be passed in a sheet conveying direction through a nip formed between the roller and the portion of the endless belt and an image on the sheet can be fixed thereto, wherein the heating member includes a first heat generating member group, a second heat generating member group and a third heat generating member group that are disposed along the width direction, and the first heat generating member group is independently operable from the second and third heat generating member groups, wherein the fixing device further comprises a switching unit of electric conduction with respect to each heat generating member groups (361-1, 361-2, 361-3), the first heat generating member group is provided at a center in the width direction, the second heat generating member group is arranged on an outside of the first heat generating member group in the width direction and the third heat generating member group is arranged on an outside of the second heat generating member group in the width direction, heat generating members of the second heat generating member group are arranged symmetrically on both outer sides of the first heat generating member group in the width direction, and heat generating members of the third heat generating member group are arranged symmetrically on both outer sides of the first heat generating member group in the width direction; characterized in that a pair of heat generating members of the second heat generating member group arranged symmetrically on both outer sides of the first heat generating member group are connected in series, a pair of heat generating members of the third heat generating member group arranged symmetrically on both outer sides of the first heat generating member group are connected in series, and each pair is individually controlled by the switching unit having a plurality of switching elements corresponding to each pair.