Heater with elongated heating resistor layer

A heater comprising:

• an elongate substrate having a substrate obverse surface and a substrate reverse surface;
• a heating resistor layer formed on the substrate obverse surface;
• and
• an electrode layer formed on the substrate obverse surface and in contact with the heating resistor layer,
• wherein the electrode layer includes a first strip-shaped portion and a second strip-shaped portion extending in a longitudinal direction of the substrate and spaced apart from each other in a width direction of the substrate,
• the heating resistor layer includes at least a first main heating member and a first sub heating member, each extending in the longitudinal direction and located between the first strip-shaped portion and the second strip-shaped portion in the width direction,
• the first sub heating member has a higher temperature coefficient of resistance than a temperature coefficient of resistance of the first main heating member, and
• the first main heating member and the first sub heating member overlap with each other as viewed in the width direction, and also are in partial contact with each other in the width direction.