Abstract: A quick operating type cathode having a cathode body consisting of: a cathode sleeve and a metal substrate which is mounted at the top opening part of the cathode sleeve and the top surface of which is coated with an electron-emissive material; and a double helical coil heater which is inserted within the cathode sleeve and the surface of which is coated with an insulating material, is characterized in that said heater comprises a coil part and a pair of leg parts connected to the end part of said coil part, a dense pitch part is formed at the top of said coil part, a sparse pitch part is formed in said coil part at the side of the leg parts and the amount of said coated insulating material per unit length of the coil wire at said sparse pitch part is larger than that at said dense pitch part.