To provide a corona discharge ionizer having a simple structure and maintaining good discharge characteristics for a long period of time by suppressing adhesion of foreign matters in a gas injecting part used as a counter electrode and the tip part of an emitter.

In this corona discharge ionizer 1, a gas supply part 11 having a gas passage 11a for a gas to flow in its inside, the gas injecting part 12 which is electrically connected to the gas supply part 11 while having an injection hole 12a to inject the gas, and in which the gas passage 11a is in communication with the injection hole 12a, and an emitter 14 the tip part of which is disposed face to face with the gas injecting part 12 are provided, the emitter 14 and the gas injecting part 12 functioning as the counter electrode of the emitter 14 form a high voltage electric field to generate ions, and the ions are injected in the direction opposite to the direction of the tip part of the emitter 14 by the gas injected from the gas injecting part 12.