A heater includes: a hollow tube sealed hermetically and reduced in pressure, the interior of the hollow tube being divided by at least one partition wall into a plurality of regions arranged side by side in a longitudinal direction of the tube; an electron source provided in each of the divided regions, the electron source being supported inside the hollow tube in an electrically insulated state from the hollow tube; a power supply that applies a voltage between the hollow tube and the electron source with the electron source as a negative polarity side; and the electron source emitting electrons toward an inner periphery surface of the hollow tube to heat the hollow tube.