Heating device for image fixing

A heating device for heating a toner image on a sheet via a fixing film, comprising:

• a substrate disposed such that a first direction of the substrate orthogonal to a conveying direction of the fixing film is longitudinal;
• a first heating resistor formed by at least one heating resistor that is disposed in a manner substantially symmetrical with respect to a predetermined reference position in a second direction orthogonal to the first direction of said substrate;
• and
• a second heating resistor formed by a plurality of heating resistors that are disposed farther from the reference position in the second direction of said substrate than said first heating resistor is and are arranged in a manner substantially symmetrical with respect to the reference position,
• wherein power-supply electrodes connected to said first heating resistor and power-supply electrodes connected to said second heating resistor are all disposed at one end of said substrate in the longitudinal direction.