An indirectly heated cathode C1 comprises a heater 1, a double coil 2, a mesh member 3, and a metal oxide 10. An electrical insulating layer 4 is formed on the surface of heater 1. Heater 1 is inserted into and positioned at the inner side of double coil 2. Mesh member 3 is disposed along the length direction of double coil 2 at the outer side of double coil 2. Double coil 2 is grounded by being connected to the ground terminal of heater 1 via a lead rod 7. Metal oxide 10 is held by double coil 2 and disposed to be in contact with mesh member 3. Metal oxide 10 and mesh member 3 are exposed to the outer side of indirectly heated electrode C1 so that the surface of metal oxide 10 and the surface of mesh member 3 make up a discharge surface and mesh member 3 is in contact with the surface part of metal oxide 10.