Abstract: An ionization type smoke detector includes a detector body, a printed circuit board on the upper surface of the detector body, an electrode mount on the upper surface of the printed circuit board, an inner electrode securing the electrode mount onto the printed circuit board and which has a radioactive source, an intermediate electrode screwed onto the electrode mount in such a way as to be situated above the inner electrode, and an outer electrode covering the electrode mount, the inner electrode and the intermediate electrode. The outer electrode has a plurality of smoke inlet windows, and is fixed to the upper surface of the printed circuit board by inserting engagement members at the lower end thereof into insertion holes of the printed circuit board. The electrode mount has an FET accommodating section including a first socket, whereas a second socket is formed on the printed circuit board. Electrodes of an FET are connected to the sockets, respectively.