A heater includes a folded heater wire, a first insulator provided on the heater wire, a metal sheath provided so as to be in contact with the first insulator, a first insulating member arranged parallel to a first end part of the heater wire taken out from a first end part of the metal sheath, a second insulating member arranged parallel to the first insulating member and parallel to a second end part of the heater wire taken out from the first end part of the metal sheath, a second insulator in contact with the first and the second insulating members and the metal sheath, and a lid member covering the first insulating member, the lid member being in contact with the metal sheath, the first and the second insulating members via the second insulator, and arranged parallel to the first and the second insulating members and the metal sheath.