The present invention provides an extraction electrode and a slit electrode. In an ion source which is provided with a plurality of slit electrodes, an ion beam with balance between current amount and controllability is led out. The ion source (1) is provided with the plurality of slit electrodes (7-10) as a leading-out electrode system. Each slit electrode (7-10) comprises the following components: an electrode frame (14) with an opening (15), and a plurality of electrode rods (16) which are arranged in the opening (15). In the electrode rods (16) which form a slit electrode (7) at most upstream part in the advancing direction of the ion beam (2) from the ion source (1), a slit-shaped opening (17) formed between the adjacent electrode rods (16) is approximately frustum-shaped in the advancing direction of the ion beam (2).