A heater includes a base, a plurality of heat generators arranged on the base in parallel to a longitudinal direction of the base, a plurality of electrodes on the base, and conductor paths disposed on the base. The conductor paths are electrically connected to the heat generators and the electrodes. The conductor paths include a main conductor path connected to one of the electrodes and a branch conductor path branched from the main conductor path. At least a part of the branch conductor path has a lower electrical resistance per unit length than an electrical resistance per unit length of the main conductor path.