A heater comprises a housing, multiple heating tubes arranged in the housing, a pair of retaining members installed in the housing, and a single heating wire. The housing has two opposite ends in a longitudinal direction thereof, with the heating tubes arranged in a row along the longitudinal direction. Each retaining member is strip shaped, with one of the pair of retaining members holding first ends of each of the multiple heating tubes, and the other of the pair of retaining members holding second ends of each of the multiple heating tubes. The single heating wire passes through the multiple heating tubes in sequence.