An indirectly heated cathode for gas discharge tube C1 comprises a heater 1, a double coil 2, a plate member 3, and a metal oxide 10. An electrical insulating layer 4 is formed on the surface of heater 1. Heater 1 is disposed at the inner side of double coil 2. Plate member 3 is disposed along the length direction of double coil 2 at the inner side of double coil 2, which is to be the discharge surface side, and is electrically connected to double coil 2. Also, plate member 3 is grounded by being connected to the ground terminal of heater 1. Metal oxide 10 is held by double coil 2 and disposed to be in contact with plate member 3. Metal oxide 10 is in contact with double coil 2.