The present invention provides an ozonizer in which a discharge region may be increased without damaging ozone generating performance. In the ozonizer, electrode modules (102) having a flat plate first electrode (7), a flat plate second electrode (3) opposed to the main face of the first electrode (7), a flat plate dielectric (5) set between the first electrode (7) and the second electrode (3) and a spacer (13) forming the discharge region, are laminated. When an alternating current voltage is applied between the first electrode (7) and the second electrode (3), electric discharge is made to occur at the discharge region where oxygen gas is injected, and ozone gas is generated. In the first electrode (7), an ozone gas passage (8) for taking out the ozone gas generated at the discharge region is formed between an electrode surface facing the discharge region and a side portion. A plurality of the ozone gas passages are dispersed within the discharge region in the first electrode. The plurality of ozone gas passages (8) collect and draw out the ozone gas generated at a plurality of the discharge region locations inside the first electrode (7).