A heater connectable with an electric energy supplying portion provided with a first terminal and a second terminal, a connector portion electrically connected with the electric energy supplying portion, and an endless belt for heating an image on a sheet, wherein said heater is contactable to the belt to heat the belt, said heater comprising: an elongated substrate; at least one first electrical contact provided on said substrate and electrically connectable with the first terminal through the connector portion; a plurality of second electrical contacts (651, 661a, 661b) provided on said substrate, including at least a third electrical contact (661a, 661b) and a fourth electrical contact, and electrically connectable with the second terminal through the connector portion; a plurality of electrode portions including a first electrode portion electrically connected with said first electrical contact and second electrode portions (652, 662) electrically connected with said second electrical contacts including at least said third electrical contact (661a, 661b) and said fourth electrical contact, said first electrode portions and said second electrode portions (652, 662) being arranged alternately with predetermined gaps in a longitudinal direction of said substrate; and a plurality of heat generating portions provided between adjacent ones of said electrode portions so as to electrically connect between adjacent electrode portions, said heat generating portions being capable of generating heat by the electric power supply between adjacent electrode portions; characterized in that said first electrical contact and said second electrical contacts including at least said third electrical contact (661a, 661b) and said fourth electrical contact are all disposed in one end portion side of said substrate with respect to the longitudinal direction, wherein said first electrical contact is disposed at a position closer to one longitudinal end of said substrate than said third and fourth electrical contacts (651, 661a, 661b), wherein said first electrical contact has a widthwise dimension as measured in a widthwise direction of said substrate which is larger than a widthwise dimension of said third and fourth electrical contacts (651, 661a, 661b). an elongated substrate; at least one first electrical contact provided on said substrate and electrically connectable with the first terminal through the connector portion; a plurality of second electrical contacts (651, 661a, 661b) provided on said substrate, including at least a third electrical contact (661a, 661b) and a fourth electrical contact, and electrically connectable with the second terminal through the connector portion; a plurality of electrode portions including a first electrode portion electrically connected with said first electrical contact and second electrode portions (652, 662) electrically connected with said second electrical contacts including at least said third electrical contact (661a, 661b) and said fourth electrical contact, said first electrode portions and said second electrode portions (652, 662) being arranged alternately with predetermined gaps in a longitudinal direction of said substrate; and a plurality of heat generating portions provided between adjacent ones of said electrode portions so as to electrically connect between adjacent electrode portions, said heat generating portions being capable of generating heat by the electric power supply between adjacent electrode portions; characterized in that said first electrical contact and said second electrical contacts including at least said third electrical contact (661a, 661b) and said fourth electrical contact are all disposed in one end portion side of said substrate with respect to the longitudinal direction, wherein said first electrical contact is disposed at a position closer to one longitudinal end of said substrate than said third and fourth electrical contacts (651, 661a, 661b), wherein said first electrical contact has a widthwise dimension as measured in a widthwise direction of said substrate which is larger than a widthwise dimension of said third and fourth electrical contacts (651, 661a, 661b).