Fixing device

A fixing device, comprising:

• a heater comprising a substrate, and a heating pattern constituted by a heating resistor on the substrate;
• an endless belt configured to rotate around the heater;
• and
• a pressure roller, the endless belt being nipped between the pressure roller and the heater,
• wherein the endless belt is nipped by and between the substrate and the pressure roller to form a nip portion comprising a first portion and a second portion located apart from the first portion in a longitudinal direction of the substrate,
• wherein a length of the first portion in a moving direction of the endless belt at the nip portion is less than a length of the second portion in the moving direction,
• wherein the substrate comprises:
• a third portion located corresponding to the first portion in the longitudinal direction;
• and
• a fourth portion located corresponding to the second portion in the longitudinal direction, and
• wherein a length of the third portion in the moving direction is less than a length of the fourth portion in the moving direction.